8 <object id="TOC" data="graphical-toc.svg" type="image/svg+xml"></object>
10 window.onload=function() { // Wait for the SVG to be loaded before changing it
11 var elem=document.querySelector("#TOC").contentDocument.getElementById("ConfigBox")
12 elem.style="opacity:0.93999999;fill:#ff0000;fill-opacity:0.1;stroke:#000000;stroke-width:0.35277778;stroke-linecap:round;stroke-linejoin:round;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1";
18 A number of options can be given at runtime to change the default
19 SimGrid behavior. For a complete list of all configuration options
20 accepted by the SimGrid version used in your simulator, simply pass
21 the --help configuration flag to your program. If some of the options
22 are not documented on this page, this is a bug that you should please
23 report so that we can fix it. Note that some of the options presented
24 here may not be available in your simulators, depending on the
25 :ref:`compile-time options <install_src_config>` that you used.
27 Setting Configuration Items
28 ---------------------------
30 There is several way to pass configuration options to the simulators.
31 The most common way is to use the ``--cfg`` command line argument. For
32 example, to set the item ``Item`` to the value ``Value``, simply
33 type the following on the command-line:
35 .. code-block:: console
37 $ my_simulator --cfg=Item:Value (other arguments)
39 Several ``--cfg`` command line arguments can naturally be used. If you
40 need to include spaces in the argument, don't forget to quote the
41 argument. You can even escape the included quotes (write ``@'`` for ``'`` if
42 you have your argument between simple quotes).
44 Another solution is to use the ``<config>`` tag in the platform file. The
45 only restriction is that this tag must occur before the first
46 platform element (be it ``<zone>``, ``<cluster>``, ``<peer>`` or whatever).
47 The ``<config>`` tag takes an ``id`` attribute, but it is currently
48 ignored so you don't really need to pass it. The important part is that
49 within that tag, you can pass one or several ``<prop>`` tags to specify
50 the configuration to use. For example, setting ``Item`` to ``Value``
51 can be done by adding the following to the beginning of your platform
57 <prop id="Item" value="Value"/>
60 A last solution is to pass your configuration directly in your program
61 with :cpp:func:`simgrid::s4u::Engine::set_config`.
65 #include <simgrid/s4u.hpp>
67 int main(int argc, char *argv[]) {
68 simgrid::s4u::Engine e(&argc, argv);
70 simgrid::s4u::Engine::set_config("Item:Value");
77 Existing Configuration Items
78 ----------------------------
81 The full list can be retrieved by passing ``--help`` and
82 ``--help-cfg`` to an executable that uses SimGrid. Try passing
83 ``help`` as a value to get the list of values accepted by a given
84 option. For example, ``--cfg=plugin:help`` will give you the list
85 of plugins available in your installation of SimGrid.
87 - **bmf/max-iterations:** :ref:`cfg=bmf/max-iterations`
88 - **bmf/precision:** :ref:`cfg=bmf/precision`
90 - **contexts/factory:** :ref:`cfg=contexts/factory`
91 - **contexts/guard-size:** :ref:`cfg=contexts/guard-size`
92 - **contexts/nthreads:** :ref:`cfg=contexts/nthreads`
93 - **contexts/stack-size:** :ref:`cfg=contexts/stack-size`
94 - **contexts/synchro:** :ref:`cfg=contexts/synchro`
96 - **cpu/maxmin-selective-update:** :ref:`Cpu Optimization Level <options_model_optim>`
97 - **cpu/model:** :ref:`options_model_select`
98 - **cpu/optim:** :ref:`Cpu Optimization Level <options_model_optim>`
100 - **debug/breakpoint:** :ref:`cfg=debug/breakpoint`
101 - **debug/clean-atexit:** :ref:`cfg=debug/clean-atexit`
102 - **debug/verbose-exit:** :ref:`cfg=debug/verbose-exit`
104 - **exception/cutpath:** :ref:`cfg=exception/cutpath`
106 - **host/model:** :ref:`options_model_select`
108 - **maxmin/concurrency-limit:** :ref:`cfg=maxmin/concurrency-limit`
110 - **model-check:** :ref:`options_modelchecking`
111 - **model-check/checkpoint:** :ref:`cfg=model-check/checkpoint`
112 - **model-check/communications-determinism:** :ref:`cfg=model-check/communications-determinism`
113 - **model-check/dot-output:** :ref:`cfg=model-check/dot-output`
114 - **model-check/max-depth:** :ref:`cfg=model-check/max-depth`
115 - **model-check/property:** :ref:`cfg=model-check/property`
116 - **model-check/reduction:** :ref:`cfg=model-check/reduction`
117 - **model-check/replay:** :ref:`cfg=model-check/replay`
118 - **model-check/send-determinism:** :ref:`cfg=model-check/send-determinism`
119 - **model-check/setenv:** :ref:`cfg=model-check/setenv`
120 - **model-check/termination:** :ref:`cfg=model-check/termination`
121 - **model-check/timeout:** :ref:`cfg=model-check/timeout`
122 - **model-check/visited:** :ref:`cfg=model-check/visited`
124 - **network/bandwidth-factor:** :ref:`cfg=network/bandwidth-factor`
125 - **network/crosstraffic:** :ref:`cfg=network/crosstraffic`
126 - **network/latency-factor:** :ref:`cfg=network/latency-factor`
127 - **network/loopback-lat:** :ref:`cfg=network/loopback`
128 - **network/loopback-bw:** :ref:`cfg=network/loopback`
129 - **network/maxmin-selective-update:** :ref:`Network Optimization Level <options_model_optim>`
130 - **network/model:** :ref:`options_model_select`
131 - **network/optim:** :ref:`Network Optimization Level <options_model_optim>`
132 - **network/TCP-gamma:** :ref:`cfg=network/TCP-gamma`
133 - **network/weight-S:** :ref:`cfg=network/weight-S`
135 - **ns3/TcpModel:** :ref:`options_pls`
136 - **ns3/seed:** :ref:`options_pls`
137 - **path:** :ref:`cfg=path`
138 - **plugin:** :ref:`cfg=plugin`
140 - **storage/max_file_descriptors:** :ref:`cfg=storage/max_file_descriptors`
142 - **precision/timing:** :ref:`cfg=precision/timing`
143 - **precision/work-amount:** :ref:`cfg=precision/work-amount`
145 - **For collective operations of SMPI,** please refer to Section :ref:`cfg=smpi/coll-selector`
146 - **smpi/auto-shared-malloc-thresh:** :ref:`cfg=smpi/auto-shared-malloc-thresh`
147 - **smpi/async-small-thresh:** :ref:`cfg=smpi/async-small-thresh`
148 - **smpi/barrier-finalization:** :ref:`cfg=smpi/barrier-finalization`
149 - **smpi/barrier-collectives:** :ref:`cfg=smpi/barrier-collectives`
150 - **smpi/buffering:** :ref:`cfg=smpi/buffering`
151 - **smpi/coll-selector:** :ref:`cfg=smpi/coll-selector`
152 - **smpi/comp-adjustment-file:** :ref:`cfg=smpi/comp-adjustment-file`
153 - **smpi/cpu-threshold:** :ref:`cfg=smpi/cpu-threshold`
154 - **smpi/display-allocs:** :ref:`cfg=smpi/display-allocs`
155 - **smpi/display-timing:** :ref:`cfg=smpi/display-timing`
156 - **smpi/errors-are-fatal:** :ref:`cfg=smpi/errors-are-fatal`
157 - **smpi/grow-injected-times:** :ref:`cfg=smpi/grow-injected-times`
158 - **smpi/host-speed:** :ref:`cfg=smpi/host-speed`
159 - **smpi/IB-penalty-factors:** :ref:`cfg=smpi/IB-penalty-factors`
160 - **smpi/iprobe:** :ref:`cfg=smpi/iprobe`
161 - **smpi/iprobe-cpu-usage:** :ref:`cfg=smpi/iprobe-cpu-usage`
162 - **smpi/init:** :ref:`cfg=smpi/init`
163 - **smpi/keep-temps:** :ref:`cfg=smpi/keep-temps`
164 - **smpi/ois:** :ref:`cfg=smpi/ois`
165 - **smpi/or:** :ref:`cfg=smpi/or`
166 - **smpi/os:** :ref:`cfg=smpi/os`
167 - **smpi/papi-events:** :ref:`cfg=smpi/papi-events`
168 - **smpi/pedantic:** :ref:`cfg=smpi/pedantic`
169 - **smpi/privatization:** :ref:`cfg=smpi/privatization`
170 - **smpi/privatize-libs:** :ref:`cfg=smpi/privatize-libs`
171 - **smpi/send-is-detached-thresh:** :ref:`cfg=smpi/send-is-detached-thresh`
172 - **smpi/shared-malloc:** :ref:`cfg=smpi/shared-malloc`
173 - **smpi/shared-malloc-hugepage:** :ref:`cfg=smpi/shared-malloc-hugepage`
174 - **smpi/simulate-computation:** :ref:`cfg=smpi/simulate-computation`
175 - **smpi/test:** :ref:`cfg=smpi/test`
176 - **smpi/wtime:** :ref:`cfg=smpi/wtime`
177 - **smpi/list-leaks** :ref:`cfg=smpi/list-leaks`
179 - **Tracing configuration options** can be found in Section :ref:`tracing_tracing_options`
181 - **storage/model:** :ref:`options_model_select`
183 - **vm/model:** :ref:`options_model_select`
187 Configuring the Platform Models
188 -------------------------------
190 .. _options_model_select:
192 Choosing the Platform Models
193 ............................
195 SimGrid comes with several network, CPU and disk models built in,
196 and you can change the used model at runtime by changing the passed
197 configuration. The three main configuration items are given below.
198 For each of these items, passing the special ``help`` value gives you
199 a short description of all possible values (for example,
200 ``--cfg=network/model:help`` will present all provided network
201 models). Also, ``--help-models`` should provide information about all
202 models for all existing resources.
204 - ``network/model``: specify the used network model. Possible values:
206 - **LV08 (default one):** Realistic network analytic model
207 (slow-start modeled by multiplying latency by 13.01, bandwidth by
208 .97; bottleneck sharing uses a payload of S=20537 for evaluating
209 RTT). Described in `Accuracy Study and Improvement of Network
210 Simulation in the SimGrid Framework
211 <http://mescal.imag.fr/membres/arnaud.legrand/articles/simutools09.pdf>`_.
212 - **Constant:** Simplistic network model where all communication
213 take a constant time (one second). This model provides the lowest
214 realism, but is (marginally) faster.
215 - **SMPI:** Realistic network model specifically tailored for HPC
216 settings (accurate modeling of slow start with correction factors on
217 three intervals: < 1KiB, < 64 KiB, >= 64 KiB). This model can be
218 :ref:`further configured <options_model_network>`.
219 - **IB:** Realistic network model specifically tailored for HPC
220 settings with InfiniBand networks (accurate modeling contention
221 behavior, based on the model explained in `this PhD work
222 <http://mescal.imag.fr/membres/jean-marc.vincent/index.html/PhD/Vienne.pdf>`_.
223 This model can be :ref:`further configured <options_model_network>`.
224 - **CM02:** Legacy network analytic model. Very similar to LV08, but
225 without corrective factors. The timings of small messages are thus
226 poorly modeled. This model is described in `A Network Model for
227 Simulation of Grid Application
228 <https://hal.inria.fr/inria-00071989/document>`_.
229 - **ns-3** (only available if you compiled SimGrid accordingly):
230 Use the packet-level network
231 simulators as network models (see :ref:`models_ns3`).
232 This model can be :ref:`further configured <options_pls>`.
234 - ``cpu/model``: specify the used CPU model. We have only one model for now:
236 - **Cas01:** Simplistic CPU model (time=size/speed)
238 - ``host/model``: we have two such models for now.
240 - **default:** Default host model. It simply uses the otherwise configured models for cpu, disk and network (i.e. CPU:Cas01,
241 disk:S19 and network:LV08 by default)
242 - **ptask_L07:** This model is mandatory if you plan to use parallel tasks (and useless otherwise). ptasks are intended to
243 model the moldable tasks of the grid scheduling literature. A specific host model is necessary because each such activity
244 has a both compute and communicate components, so the CPU and network models must be mixed together.
246 - ``storage/model``: specify the used storage model. Only one model is
248 - ``vm/model``: specify the model for virtual machines. Only one model
251 .. todo: make 'compound' the default host model.
253 .. _options_model_solver:
258 The different models rely on a linear inequalities solver to share
259 the underlying resources. SimGrid allows you to change the solver, but
260 be cautious, **don't change it unless you are 100% sure**.
262 - items ``cpu/solver``, ``network/solver``, ``disk/solver`` and ``host/solver``
263 allow you to change the solver for each model:
265 - **maxmin:** The default solver for all models except ptask. Provides a
266 max-min fairness allocation.
267 - **fairbottleneck:** The default solver for ptasks. Extends max-min to
268 allow heterogeneous resources.
269 - **bmf:** More realistic solver for heterogeneous resource sharing.
270 Implements BMF (Bottleneck max fairness) fairness. To be used with
271 parallel tasks instead of fair-bottleneck.
273 .. _options_model_optim:
278 The network and CPU models that are based on linear inequalities solver (that
279 is, all our analytical models) accept specific optimization
282 - items ``network/optim`` and ``cpu/optim`` (both default to 'Lazy'):
284 - **Lazy:** Lazy action management (partial invalidation in lmm +
285 heap in action remaining).
286 - **TI:** Trace integration. Highly optimized mode when using
287 availability traces (only available for the Cas01 CPU model for
289 - **Full:** Full update of remaining and variables. Slow but may be
290 useful when debugging.
292 - items ``network/maxmin-selective-update`` and
293 ``cpu/maxmin-selective-update``: configure whether the underlying
294 should be lazily updated or not. It should have no impact on the
295 computed timings, but should speed up the computation. |br| It is
296 still possible to disable this feature because it can reveal
297 counter-productive in very specific scenarios where the
298 interaction level is high. In particular, if all your
299 communication share a given backbone link, you should disable it:
300 without it, a simple regular loop is used to update each
301 communication. With it, each of them is still updated (because of
302 the dependency induced by the backbone), but through a complicated
303 and slow pattern that follows the actual dependencies.
305 .. _cfg=bmf/precision:
306 .. _cfg=precision/timing:
307 .. _cfg=precision/work-amount:
312 **Option** ``precision/timing`` **Default:** 1e-9 (in seconds) |br|
313 **Option** ``precision/work-amount`` **Default:** 1e-5 (in flops or bytes) |br|
314 **Option** ``bmf/precision`` **Default:** 1e-12 (no unit)
316 The analytical models handle a lot of floating point values. It is
317 possible to change the epsilon used to update and compare them through
318 this configuration item. Changing it may speedup the simulation by
319 discarding very small actions, at the price of a reduced numerical
320 precision. You can modify separately the precision used to manipulate
321 timings (in seconds) and the one used to manipulate amounts of work
324 .. _cfg=maxmin/concurrency-limit:
329 **Option** ``maxmin/concurrency-limit`` **Default:** -1 (no limit)
331 The maximum number of variables per resource can be tuned through this
332 option. You can have as many simultaneous actions per resources as you
333 want. If your simulation presents a very high level of concurrency, it
334 may help to use e.g. 100 as a value here. It means that at most 100
335 actions can consume a resource at a given time. The extraneous actions
336 are queued and wait until the amount of concurrency of the considered
337 resource lowers under the given boundary.
339 Such limitations help both to the simulation speed and simulation accuracy
340 on highly constrained scenarios, but the simulation speed suffers of this
341 setting on regular (less constrained) scenarios so it is off by default.
343 .. _cfg=bmf/max-iterations:
348 **Option** ``bmf/max-iterations`` **Default:** 1000
350 It may happen in some settings that the BMF solver fails to converge to
351 a solution, so there is a hard limit on the amount of iteration count to
352 avoid infinite loops.
354 .. _options_model_network:
356 Configuring the Network Model
357 .............................
359 .. _cfg=network/TCP-gamma:
361 Maximal TCP Window Size
362 ^^^^^^^^^^^^^^^^^^^^^^^
364 **Option** ``network/TCP-gamma`` **Default:** 4194304
366 The analytical models need to know the maximal TCP window size to take the TCP congestion mechanism into account (see
367 :ref:`this page <understanding_cm02>` for details). On Linux, this value can be retrieved using the following commands.
368 Both give a set of values, and you should use the last one, which is the maximal size.
370 .. code-block:: console
372 $ cat /proc/sys/net/ipv4/tcp_rmem # gives the sender window
373 $ cat /proc/sys/net/ipv4/tcp_wmem # gives the receiver window
375 If you want to disable the TCP windowing mechanism, set this parameter to 0.
377 .. _cfg=network/bandwidth-factor:
378 .. _cfg=network/latency-factor:
379 .. _cfg=network/weight-S:
381 Manual calibration factors
382 ^^^^^^^^^^^^^^^^^^^^^^^^^^
384 SimGrid can take network irregularities such as a slow startup or changing behavior depending on the message size into account.
385 The values provided by default were computed a long time ago through data fitting one the timings of either packet-level
386 simulators or direct experiments on real platforms. These default values should be OK for most users, but if simulation realism
387 is really important to you, you probably want to recalibrate the models (i.e., devise sensible values for your specific
388 settings). This section only describes how to pass new values to the models while the calibration process involved in the
389 computation of these values is described :ref:`in the relevant chapter <models_calibration>`.
391 We found out that many networking effects can be realistically accounted for with the three following correction factors. They
392 were shown to be enough to capture slow-start effects, the different transmission modes of MPI systems (eager vs. rendez-vous
393 mode), or the non linear effects of wifi sharing.
395 **Option** ``network/latency-factor`` **Default:** 1.0, but overridden by most models
397 This option specifies a multiplier to apply to the *physical* latency (i.e., the one described in the platform) of the set of
398 links involved in a communication. The factor can either be a constant to apply to any communication, or it may depend on the
399 message size. The ``CM02`` model does not use any correction factor, so the latency-factor remains to 1. The ``LV08`` model sets
400 it to 13.01 to model slow-start, while the ``SMPI`` model has several possible values depending on the interval in which the
401 message size falls. The default SMPI setting given below specifies for example that a message smaller than 257 bytes will get a
402 latency multiplier of 2.01467 while a message whose size is in [15424, 65472] will get a latency multiplier of 3.48845. The
403 ``wifi`` model goes further and uses a callback in the program to compute the factor that must be non-linear in this case.
405 This multiplier is applied to the latency computed from the platform, that is the sum of all link *physical* latencies over the
406 :ref:`network path <platform_routing>` used by the considered communication, to derive the *effective* end-to-end latency.
408 Constant factors are easy to express, but the interval-based syntax used in SMPI is somewhat complex. It expects a set of
409 factors separated by semicolons, each of the form ``boundary:factor``. For example if your specification is
410 ``0:1;1000:2;5000:3``, it means that on [0, 1000) the factor is 1. On [1000,5000), the factor is 2 while the factor is 3 for
411 5000 and beyond. If your first interval does include size=0, then the default value of 1 is used before. Changing the factor
412 callback is not possible from the command line and must be done from your code, as shown in `this example
413 <https://framagit.org/simgrid/simgrid/tree/master/examples/cpp/network-factors/s4u-network-factors.cpp>`_. Note that the chosen
414 model only provides some default settings. You may pick a ``LV08`` model to get some of the settings, and override the latency
415 with interval-based values.
417 SMPI default value: 65472:11.6436; 15424:3.48845; 9376:2.59299; 5776:2.18796; 3484:1.88101; 1426:1.61075; 732:1.9503;
418 257:1.95341;0:2.01467 (interval boundaries are sorted automatically). These values were computed by data fitting on the Stampede
419 Supercomputer at TACC, with optimal deployment of processes on nodes. To accurately model your settings, you should redo the
420 :ref:`calibration <models_calibration>`.
422 **Option** ``network/bandwidth-factor`` **Default:** 1.0, but overridden by most models
424 Setting this option automatically adjusts the *effective* bandwidth (i.e., the one perceived by the application) used by any
425 given communication. As with latency-factor above, the value can be a constant (``CM02`` uses 1 -- no correction -- while
426 ``LV08`` uses 0.97 to discount TCP headers while computing the payload bandwidth), interval-based (as the default provided by
427 the ``SMPI``), or using in-program callbacks (as with ``wifi``).
429 SMPI default value: 65472:0.940694;15424:0.697866;9376:0.58729;5776:1.08739;3484:0.77493;1426:0.608902;732:0.341987;257:0.338112;0:0.812084
430 This was also computed on the Stampede Supercomputer.
432 **Option** ``network/weight-S`` **Default:** depends on the model
434 Value used to account for RTT-unfairness when sharing a bottleneck (network connections with a large RTT are generally penalized
435 against those with a small one). See :ref:`models_TCP` and also this scientific paper: `Accuracy Study and Improvement of Network
436 Simulation in the SimGrid Framework <http://mescal.imag.fr/membres/arnaud.legrand/articles/simutools09.pdf>`_
438 Default values for ``CM02`` is 0. ``LV08`` sets it to 20537 while both ``SMPI`` and ``IB`` set it to 8775.
440 .. _cfg=network/loopback:
442 Configuring loopback link
443 ^^^^^^^^^^^^^^^^^^^^^^^^^
445 Several network models provide an implicit loopback link to account for local
446 communication on a host. By default it has a 10GBps bandwidth and a null latency.
447 This can be changed with ``network/loopback-lat`` and ``network/loopback-bw``
448 items. Note that this loopback is conveniently modeled with a :ref:`single FATPIPE link <pf_loopback>`
449 for the whole platform. If modeling contention inside nodes is important then you should
450 rather add such loopback links (one for each host) yourself.
452 .. _cfg=smpi/IB-penalty-factors:
457 InfiniBand network behavior can be modeled through 3 parameters
458 ``smpi/IB-penalty-factors:"βe;βs;γs"``, as explained in `the PhD
459 thesis of Jérôme Vienne
460 <http://mescal.imag.fr/membres/jean-marc.vincent/index.html/PhD/Vienne.pdf>`_ (in French)
461 or more concisely in `this paper <https://hal.inria.fr/hal-00953618/document>`_,
462 even if that paper does only describe models for myrinet and ethernet.
463 You can see in Fig 2 some results for Infiniband, for example. This model
464 may be outdated by now for modern infiniband, anyway, so a new
465 validation would be good.
467 The three paramaters are defined as follows:
469 - βs: penalty factor for outgoing messages, computed by running a simple send to
470 two nodes and checking slowdown compared to a single send to one node,
472 - βe: penalty factor for ingoing messages, same computation method but with one
473 node receiving several messages
474 - γr: slowdown factor when communication buffer memory is saturated. It needs a
475 more complicated pattern to run in order to be computed (5.3 in the thesis,
476 page 107), and formula in the end is γr = time(c)/(3×βe×time(ref)), where
477 time(ref) is the time of a single comm with no contention).
479 Once these values are computed, a penalty is assessed for each message (this is
480 the part implemented in the simulator) as shown page 106 of the thesis. Here is
481 a simple translation of this text. First, some notations:
483 - ∆e(e) which corresponds to the incoming degree of node e, that is to say the number of communications having as destination node e.
484 - ∆s (s) which corresponds to the degree outgoing from node s, that is to say the number of communications sent by node s.
485 - Φ (e) which corresponds to the number of communications destined for the node e but coming from a different node.
486 - Ω (s, e) which corresponds to the number of messages coming from node s to node e. If node e only receives communications from different nodes then Φ (e) = ∆e (e). On the other hand if, for example, there are three messages coming from node s and going from node e then Φ (e) 6 = ∆e (e) and Ω (s, e) = 3
488 To determine the penalty for a communication, two values need to be calculated. First, the penalty caused by the conflict in transmission, noted ps.
491 - if ∆s (i) = 1 then ps = 1.
492 - if ∆s (i) ≥ 2 and ∆e (i) ≥ 3 then ps = ∆s (i) × βs × γr
493 - else, ps = ∆s (i) × βs
496 Then, the penalty caused by the conflict in reception (noted pe) should be computed as follows:
498 - if ∆e (i) = 1 then pe = 1
499 - else, pe = Φ (e) × βe × Ω (s, e)
501 Finally, the penalty associated with the communication is:
502 p = max (ps ∈ s, pe)
504 .. _cfg=network/crosstraffic:
506 Simulating Cross-Traffic
507 ^^^^^^^^^^^^^^^^^^^^^^^^
509 Since SimGrid v3.7, cross-traffic effects can be taken into account in
510 analytical simulations. It means that ongoing and incoming
511 communication flows are treated independently. In addition, the LV08
512 model adds 0.05 of usage on the opposite direction for each new
513 created flow. This can be useful to simulate some important TCP
514 phenomena such as ack compression.
516 For that to work, your platform must have two links for each
517 pair of interconnected hosts. An example of usable platform is
518 available in ``examples/platforms/crosstraffic.xml``.
520 This is activated through the ``network/crosstraffic`` item, that
521 can be set to 0 (disable this feature) or 1 (enable it).
523 Note that with the default host model this option is activated by default.
525 .. _cfg=smpi/async-small-thresh:
527 Simulating Asynchronous Send
528 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
530 (this configuration item is experimental and may change or disappear)
532 It is possible to specify that messages below a certain size (in bytes) will be
533 sent as soon as the call to MPI_Send is issued, without waiting for
534 the correspondent receive. This threshold can be configured through
535 the ``smpi/async-small-thresh`` item. The default value is 0. This
536 behavior can also be manually set for mailboxes, by setting the
537 receiving mode of the mailbox with a call to
538 :cpp:func:`sg_mailbox_set_receiver`. After this, all messages sent to
539 this mailbox will have this behavior regardless of the message size.
541 This value needs to be smaller than or equals to the threshold set at
542 :ref:`cfg=smpi/send-is-detached-thresh`, because asynchronous messages
543 are meant to be detached as well.
550 **Option** ``ns3/TcpModel`` **Default:** "default" (ns-3 default)
552 When using ns-3, there is an extra item ``ns3/TcpModel``, corresponding
553 to the ``ns3::TcpL4Protocol::SocketType`` configuration item in
554 ns-3. The only valid values (enforced on the SimGrid side) are
555 'default' (no change to the ns-3 configuration), 'NewReno' or 'Reno' or
558 **Option** ``ns3/seed`` **Default:** "" (don't set the seed in ns-3)
560 This option is the random seed to provide to ns-3 with
561 ``ns3::RngSeedManager::SetSeed`` and ``ns3::RngSeedManager::SetRun``.
563 If left blank, no seed is set in ns-3. If the value 'time' is
564 provided, the current amount of seconds since epoch is used as a seed.
565 Otherwise, the provided value must be a number to use as a seed.
567 Configuring the Storage model
568 .............................
570 .. _cfg=storage/max_file_descriptors:
572 File Descriptor Count per Host
573 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
575 **Option** ``storage/max_file_descriptors`` **Default:** 1024
577 Each host maintains a fixed-size array of its file descriptors. You
578 can change its size through this item to either enlarge it if your
579 application requires it or to reduce it to save memory space.
586 SimGrid plugins allow one to extend the framework without changing its
587 source code directly. Read the source code of the existing plugins to
588 learn how to do so (in ``src/plugins``), and ask your questions to the
589 usual channels (Stack Overflow, Mailing list, IRC). The basic idea is
590 that plugins usually register callbacks to some signals of interest.
591 If they need to store some information about a given object (Link, CPU
592 or Actor), they do so through the use of a dedicated object extension.
594 Some of the existing plugins can be activated from the command line,
595 meaning that you can activate them from the command line without any
596 modification to your simulation code. For example, you can activate
597 the host energy plugin by adding ``--cfg=plugin:host_energy`` to your
600 Here is a partial list of plugins that can be activated this way. You can get
601 the full list by passing ``--cfg=plugin:help`` to your simulator.
603 - :ref:`Host Energy <plugin_host_energy>`: models the energy dissipation of the compute units.
604 - :ref:`Link Energy <plugin_link_energy>`: models the energy dissipation of the network.
605 - :ref:`Host Load <plugin_host_load>`: monitors the load of the compute units.
607 .. _options_modelchecking:
609 Configuring the Model-Checking
610 ------------------------------
612 To enable SimGrid's model-checking support, the program should
613 be executed using the simgrid-mc wrapper:
615 .. code-block:: console
617 $ simgrid-mc ./my_program
619 Safety properties are expressed as assertions using the function
620 :cpp:func:`void MC_assert(int prop)`.
622 .. _cfg=smpi/buffering:
624 Specifying the MPI buffering behavior
625 .....................................
627 **Option** ``smpi/buffering`` **Default:** infty
629 Buffering in MPI has a huge impact on the communication semantic. For example,
630 standard blocking sends are synchronous calls when the system buffers are full
631 while these calls can complete immediately without even requiring a matching
632 receive call for small messages sent when the system buffers are empty.
634 In SMPI, this depends on the message size, that is compared against two thresholds:
636 - if (size < :ref:`smpi/async-small-thresh <cfg=smpi/async-small-thresh>`) then
637 MPI_Send returns immediately, and the message is sent even if the
638 corresponding receive has not be issued yet. This is known as the eager mode.
639 - if (:ref:`smpi/async-small-thresh <cfg=smpi/async-small-thresh>` < size <
640 :ref:`smpi/send-is-detached-thresh <cfg=smpi/send-is-detached-thresh>`) then
641 MPI_Send also returns immediately, but SMPI waits for the corresponding
642 receive to be posted, in order to perform the communication operation.
643 - if (:ref:`smpi/send-is-detached-thresh <cfg=smpi/send-is-detached-thresh>` < size) then
644 MPI_Send returns only when the message has actually been sent over the network. This is known as the rendez-vous mode.
646 The ``smpi/buffering`` (only valid with MC) option gives an easier interface to choose between these semantics. It can take two values:
648 - **zero:** means that buffering should be disabled. All communications are actually blocking.
649 - **infty:** means that buffering should be made infinite. All communications are non-blocking.
651 .. _cfg=model-check/property:
653 Specifying a liveness property
654 ..............................
656 **Option** ``model-check/property`` **Default:** unset
658 If you want to specify liveness properties, you have to pass them on
659 the command line, specifying the name of the file containing the
660 property, as formatted by the `ltl2ba <https://github.com/utwente-fmt/ltl2ba>`_ program.
661 Note that ltl2ba is not part of SimGrid and must be installed separately.
663 .. code-block:: console
665 $ simgrid-mc ./my_program --cfg=model-check/property:<filename>
667 .. _cfg=model-check/checkpoint:
669 Going for Stateful Verification
670 ...............................
672 By default, the system is backtracked to its initial state to explore
673 another path, instead of backtracking to the exact step before the fork
674 that we want to explore (this is called stateless verification). This
675 is done this way because saving intermediate states can rapidly
676 exhaust the available memory. If you want, you can change the value of
677 the ``model-check/checkpoint`` item. For example,
678 ``--cfg=model-check/checkpoint:1`` asks to take a checkpoint every
679 step. Beware, this will certainly explode your memory. Larger values
680 are probably better, make sure to experiment a bit to find the right
681 setting for your specific system.
683 .. _cfg=model-check/reduction:
685 Specifying the kind of reduction
686 ................................
688 The main issue when using the model-checking is the state space
689 explosion. You can activate some reduction technique with
690 ``--cfg=model-check/reduction:<technique>``. For now, this
691 configuration variable can take 2 values:
693 - **none:** Do not apply any kind of reduction (mandatory for
694 liveness properties, as our current DPOR algorithm breaks cycles)
695 - **dpor:** Apply Dynamic Partial Ordering Reduction. Only valid if
696 you verify local safety properties (default value for safety
699 Another way to mitigate the state space explosion is to search for
700 cycles in the exploration with the :ref:`cfg=model-check/visited`
701 configuration. Note that DPOR and state-equality reduction may not
702 play well together. You should choose between them.
704 Our current DPOR implementation could be improved in may ways. We are
705 currently improving its efficiency (both in term of reduction ability
706 and computational speed), and future work could make it compatible
707 with liveness properties.
709 .. _cfg=model-check/visited:
711 Size of Cycle Detection Set (state equality reduction)
712 ......................................................
714 Mc SimGrid can be asked to search for cycles during the exploration,
715 i.e. situations where a new explored state is in fact the same state
716 than a previous one.. This can prove useful to mitigate the state
717 space explosion with safety properties, and this is the crux when
718 searching for counter-examples to the liveness properties.
720 Note that this feature may break the current implementation of the
721 DPOR reduction technique.
723 The ``model-check/visited`` item is the maximum number of states, which
724 are stored in memory. If the maximum number of snapshotted state is
725 reached, some states will be removed from the memory and some cycles
726 might be missed. Small values can lead to incorrect verifications, but
727 large values can exhaust your memory and be CPU intensive as each new
728 state must be compared to that amount of older saved states.
730 The default settings depend on the kind of exploration. With safety
731 checking, no state is snapshotted and cycles cannot be detected. With
732 liveness checking, all states are snapshotted because missing a cycle
733 could hinder the exploration soundness.
735 .. _cfg=model-check/termination:
737 Non-Termination Detection
738 .........................
740 The ``model-check/termination`` configuration item can be used to
741 report if a non-termination execution path has been found. This is a
742 path with a cycle, which means that the program might never terminate.
744 This only works in safety mode, not in liveness mode.
746 This options is disabled by default.
748 .. _cfg=model-check/dot-output:
753 If set, the ``model-check/dot-output`` configuration item is the name
754 of a file in which to write a dot file of the path leading to the
755 property violation discovered (safety or liveness violation), as well
756 as the cycle for liveness properties. This dot file can then be fed to the
757 graphviz dot tool to generate a corresponding graphical representation.
759 .. _cfg=model-check/max-depth:
761 Exploration Depth Limit
762 .......................
764 The ``model-check/max-depth`` can set the maximum depth of the
765 exploration graph of the model checker. If this limit is reached, a
766 logging message is sent and the results might not be exact.
768 By default, the exploration is limited to the depth of 1000.
770 .. _cfg=model-check/timeout:
775 By default, the model checker does not handle timeout conditions: the `wait`
776 operations never time out. With the ``model-check/timeout`` configuration item
777 set to **yes**, the model checker will explore timeouts of `wait` operations.
779 .. _cfg=model-check/communications-determinism:
780 .. _cfg=model-check/send-determinism:
782 Communication Determinism
783 .........................
785 The ``model-check/communications-determinism`` and
786 ``model-check/send-determinism`` items can be used to select the
787 communication determinism mode of the model checker, which checks
788 determinism properties of the communications of an application.
790 .. _cfg=model-check/setenv:
792 Passing environment variables
793 .............................
795 You can specify extra environment variables to be set in the verified application
796 with ``model-check/setenv``. For example, you can preload a library as follows:
797 ``-cfg=model-check/setenv:LD_PRELOAD=toto;LD_LIBRARY_PATH=/tmp``.
801 Verification Performance Considerations
802 .......................................
804 The size of the stacks can have a huge impact on the memory
805 consumption when using model-checking. By default, each snapshot will
806 save a copy of the whole stacks and not only of the part that is
807 really meaningful: you should expect the contribution of the memory
808 consumption of the snapshots to be:
809 :math:`\text{number of processes} \times \text{stack size} \times \text{number of states}`.
811 When compiled against the model checker, the stacks are not
812 protected with guards: if the stack size is too small for your
813 application, the stack will silently overflow into other parts of the
814 memory (see :ref:`contexts/guard-size <cfg=contexts/guard-size>`).
816 .. _cfg=model-check/replay:
818 Replaying buggy execution paths from the model checker
819 ......................................................
821 Debugging the problems reported by the model checker is challenging:
822 First, the application under verification cannot be debugged with gdb
823 because the model checker already traces it. Then, the model checker may
824 explore several execution paths before encountering the issue, making it
825 very difficult to understand the output. Fortunately, SimGrid provides
826 the execution path leading to any reported issue so that you can replay
827 this path reported by the model checker, enabling the usage of classical
830 When the model checker finds an interesting path in the application
831 execution graph (where a safety or liveness property is violated), it
832 generates an identifier for this path. Here is an example of the output:
834 .. code-block:: console
836 [ 0.000000] (0:@) Check a safety property
837 [ 0.000000] (0:@) **************************
838 [ 0.000000] (0:@) *** PROPERTY NOT VALID ***
839 [ 0.000000] (0:@) **************************
840 [ 0.000000] (0:@) Counter-example execution trace:
841 [ 0.000000] (0:@) [(1)Tremblay (app)] MC_RANDOM(3)
842 [ 0.000000] (0:@) [(1)Tremblay (app)] MC_RANDOM(4)
843 [ 0.000000] (0:@) Path = 1/3;1/4
844 [ 0.000000] (0:@) Expanded states = 27
845 [ 0.000000] (0:@) Visited states = 68
846 [ 0.000000] (0:@) Executed transitions = 46
848 The interesting line is ``Path = 1/3;1/4``, which means that you should use
849 ``--cfg=model-check/replay:1/3;1/4`` to replay your application on the buggy
850 execution path. All options (but the model checker related ones) must
851 remain the same. In particular, if you ran your application with
852 ``smpirun -wrapper simgrid-mc``, then do it again. Remove all
853 MC-related options, keep non-MC-related ones and add
854 ``--cfg=model-check/replay:???``.
856 Currently, if the path is of the form ``X;Y;Z``, each number denotes
857 the actor's pid that is selected at each indecision point. If it's of
858 the form ``X/a;Y/b``, the X and Y are the selected pids while the a
859 and b are the return values of their simcalls. In the previous
860 example, ``1/3;1/4``, you can see from the full output that the actor
861 1 is doing MC_RANDOM simcalls, so the 3 and 4 simply denote the values
862 that these simcall return on the execution branch leading to the
865 Configuring the User Code Virtualization
866 ----------------------------------------
868 .. _cfg=contexts/factory:
870 Selecting the Virtualization Factory
871 ....................................
873 **Option** contexts/factory **Default:** "raw"
875 In SimGrid, the user code is virtualized in a specific mechanism that
876 allows the simulation kernel to control its execution: when a user
877 process requires a blocking action (such as sending a message), it is
878 interrupted, and only gets released when the simulated clock reaches
879 the point where the blocking operation is done. This is explained
880 graphically in the `relevant tutorial, available online
881 <https://simgrid.org/tutorials/simgrid-simix-101.pdf>`_.
883 In SimGrid, the containers in which user processes are virtualized are
884 called contexts. Several context factory are provided, and you can
885 select the one you want to use with the ``contexts/factory``
886 configuration item. Some of the following may not exist on your
887 machine because of portability issues. In any case, the default one
888 should be the most effcient one (please report bugs if the
889 auto-detection fails for you). They are approximately sorted here from
890 the slowest to the most efficient:
892 - **thread:** very slow factory using full featured, standard threads.
893 They are slow but very standard. Some debuggers or profilers only work with this factory.
894 - **ucontext:** fast factory using System V contexts (Linux and FreeBSD only)
895 - **boost:** This uses the `context
896 implementation <http://www.boost.org/doc/libs/1_59_0/libs/context/doc/html/index.html>`_
897 of the boost library for a performance that is comparable to our
899 |br| Install the relevant library (e.g. with the
900 libboost-contexts-dev package on Debian/Ubuntu) and recompile
902 - **raw:** amazingly fast factory using a context switching mechanism
903 of our own, directly implemented in assembly (only available for x86
904 and amd64 platforms for now) and without any unneeded system call.
906 The main reason to change this setting is when the debugging tools become
907 fooled by the optimized context factories. Threads are the most
908 debugging-friendly contexts, as they allow one to set breakpoints
909 anywhere with gdb and visualize backtraces for all processes, in order
910 to debug concurrency issues. Valgrind is also more comfortable with
911 threads, but it should be usable with all factories (Exception: the
912 callgrind tool really dislikes raw and ucontext factories).
914 .. _cfg=contexts/stack-size:
916 Adapting the Stack Size
917 .......................
919 **Option** ``contexts/stack-size`` **Default:** 8192 KiB
921 Each virtualized used process is executed using a specific system
922 stack. The size of this stack has a huge impact on the simulation
923 scalability, but its default value is rather large. This is because
924 the error messages that you get when the stack size is too small are
925 rather disturbing: this leads to stack overflow (overwriting other
926 stacks), leading to segfaults with corrupted stack traces.
928 If you want to push the scalability limits of your code, you might
929 want to reduce the ``contexts/stack-size`` item. Its default value is
930 8192 (in KiB), while our Chord simulation works with stacks as small
931 as 16 KiB, for example. You can ensure that some actors have a specific
932 size by simply changing the value of this configuration item before
933 creating these actors. The :cpp:func:`simgrid::s4u::Engine::set_config`
934 functions are handy for that.
936 This *setting is ignored* when using the thread factory (because there
937 is no way to modify the stack size with C++ system threads). Instead,
938 you should compile SimGrid and your application with
939 ``-fsplit-stack``. Note that this compilation flag is not compatible
940 with the model checker right now.
942 The operating system should only allocate memory for the pages of the
943 stack which are actually used and you might not need to use this in
944 most cases. However, this setting is very important when using the
945 model checker (see :ref:`options_mc_perf`).
947 .. _cfg=contexts/guard-size:
949 Disabling Stack Guard Pages
950 ...........................
952 **Option** ``contexts/guard-size`` **Default** 1 page in most case (0 pages with MC)
954 Unless you use the threads context factory (see
955 :ref:`cfg=contexts/factory`), a stack guard page is usually used
956 which prevents the stack of a given actor from overflowing on another
957 stack. But the performance impact may become prohibitive when the
958 amount of actors increases. The option ``contexts/guard-size`` is the
959 number of stack guard pages used. By setting it to 0, no guard pages
960 will be used: in this case, you should avoid using small stacks (with
961 :ref:`contexts/stack-size <cfg=contexts/stack-size>`) as the stack
962 will silently overflow on other parts of the memory.
964 When no stack guard page is created, stacks may then silently overflow
965 on other parts of the memory if their size is too small for the
968 .. _cfg=contexts/nthreads:
969 .. _cfg=contexts/synchro:
971 Running User Code in Parallel
972 .............................
974 Parallel execution of the user code is only considered stable in
975 SimGrid v3.7 and higher, and mostly for S4U simulations. SMPI
976 simulations may well fail in parallel mode. It is described in
977 `INRIA RR-7653 <http://hal.inria.fr/inria-00602216/>`_.
979 If you are using the **ucontext** or **raw** context factories, you can
980 request to execute the user code in parallel. Several threads are
981 launched, each of them handling the same number of user contexts at each
982 run. To activate this, set the ``contexts/nthreads`` item to the amount
983 of cores that you have in your computer (or lower than 1 to have the
984 amount of cores auto-detected).
986 When parallel execution is activated, you can choose the
987 synchronization schema used with the ``contexts/synchro`` item,
988 which value is either:
990 - **futex:** ultra optimized synchronisation schema, based on futexes
991 (fast user-mode mutexes), and thus only available on Linux systems.
992 This is the default mode when available.
993 - **posix:** slow but portable synchronisation using only POSIX
995 - **busy_wait:** not really a synchronisation: the worker threads
996 constantly request new contexts to execute. It should be the most
997 efficient synchronisation schema, but it loads all the cores of
998 your machine for no good reason. You probably prefer the other less
1001 Configuring the Tracing
1002 -----------------------
1004 The :ref:`tracing subsystem <outcome_vizu>` can be configured in
1005 several different ways depending on the used interface (S4U, SMPI)
1006 and the kind of traces that needs to be obtained. See the
1007 :ref:`Tracing Configuration Options subsection
1008 <tracing_tracing_options>` for a full description of each
1009 configuration option.
1011 We detail here a simple way to get the traces working for you, even if
1012 you never used the tracing API.
1015 - Any SimGrid-based simulator (S4U, SMPI, ...) and raw traces:
1017 .. code-block:: none
1019 --cfg=tracing:yes --cfg=tracing/uncategorized:yes
1021 The first parameter activates the tracing subsystem, and the second
1022 tells it to trace host and link utilization (without any
1025 - S4U-based simulator and categorized traces (you need to
1026 declare categories and classify your tasks according to them)
1028 .. code-block:: none
1030 --cfg=tracing:yes --cfg=tracing/categorized:yes
1032 The first parameter activates the tracing subsystem, and the second
1033 tells it to trace host and link categorized utilization.
1035 - SMPI simulator and traces for a space/time view:
1037 .. code-block:: console
1039 $ smpirun -trace ...
1041 The `-trace` parameter for the smpirun script runs the simulation
1042 with ``--cfg=tracing:yes --cfg=tracing/smpi:yes``. Check the
1043 smpirun's `-help` parameter for additional tracing options.
1045 Sometimes you might want to put additional information on the trace to
1046 correctly identify them later, or to provide data that can be used to
1047 reproduce an experiment. You have two ways to do that:
1049 - Add a string on top of the trace file as comment:
1051 .. code-block:: none
1053 --cfg=tracing/comment:my_simulation_identifier
1055 - Add the contents of a textual file on top of the trace file as comment:
1057 .. code-block:: none
1059 --cfg=tracing/comment-file:my_file_with_additional_information.txt
1061 Please, use these two parameters (for comments) to make reproducible
1062 simulations. For additional details about this and all tracing
1063 options, check See the :ref:`tracing_tracing_options`.
1068 The SMPI interface provides several specific configuration items.
1069 These are not easy to see with ``--help-cfg``, since SMPI binaries are usually launched through the ``smiprun`` script.
1071 .. _cfg=smpi/host-speed:
1072 .. _cfg=smpi/cpu-threshold:
1073 .. _cfg=smpi/simulate-computation:
1075 Automatic Benchmarking of SMPI Code
1076 ...................................
1078 In SMPI, the sequential code is automatically benchmarked, and these
1079 computations are automatically reported to the simulator. That is to
1080 say that if you have a large computation between a ``MPI_Recv()`` and
1081 a ``MPI_Send()``, SMPI will automatically benchmark the duration of
1082 this code, and create an execution task within the simulator to take
1083 this into account. For that, the actual duration is measured on the
1084 host machine and then scaled to the power of the corresponding
1085 simulated machine. The variable ``smpi/host-speed`` allows one to
1086 specify the computational speed of the host machine (in flop/s by
1087 default) to use when scaling the execution times.
1089 The default value is ``smpi/host-speed=20kf`` (= 20,000 flop/s). This
1090 is probably underestimated for most machines, leading SimGrid to
1091 overestimate the amount of flops in the execution blocks that are
1092 automatically injected in the simulator. As a result, the execution
1093 time of the whole application will probably be overestimated until you
1094 use a realistic value.
1096 When the code consists of numerous consecutive MPI calls, the
1097 previous mechanism feeds the simulation kernel with numerous tiny
1098 computations. The ``smpi/cpu-threshold`` item becomes handy when this
1099 impacts badly on the simulation performance. It specifies a threshold (in
1100 seconds) below which the execution chunks are not reported to the
1101 simulation kernel (default value: 1e-6).
1103 .. note:: The option ``smpi/cpu-threshold`` ignores any computation
1104 time spent below this threshold. SMPI does not consider the
1105 `amount of time` of these computations; there is no offset for
1106 this. Hence, a value that is too small, may lead to unreliable
1109 In some cases, however, one may wish to disable simulation of
1110 the computation of an application. This is the case when SMPI is used not to
1111 simulate an MPI application, but instead an MPI code that performs
1112 "live replay" of another MPI app (e.g., ScalaTrace's replay tool, or
1113 various on-line simulators that run an app at scale). In this case the
1114 computation of the replay/simulation logic should not be simulated by
1115 SMPI. Instead, the replay tool or on-line simulator will issue
1116 "computation events", which correspond to the actual MPI simulation
1117 being replayed/simulated. At the moment, these computation events can
1118 be simulated using SMPI by calling internal smpi_execute*() functions.
1120 To disable the benchmarking/simulation of a computation in the simulated
1121 application, the variable ``smpi/simulate-computation`` should be set
1122 to **no**. This option just ignores the timings in your simulation; it
1123 still executes the computations itself. If you want to stop SMPI from
1124 doing that, you should check the SMPI_SAMPLE macros, documented in
1125 Section :ref:`SMPI_use_faster`.
1127 +------------------------------------+-------------------------+-----------------------------+
1128 | Solution | Computations executed? | Computations simulated? |
1129 +====================================+=========================+=============================+
1130 | --cfg=smpi/simulate-computation:no | Yes | Never |
1131 +------------------------------------+-------------------------+-----------------------------+
1132 | --cfg=smpi/cpu-threshold:42 | Yes, in all cases | If it lasts over 42 seconds |
1133 +------------------------------------+-------------------------+-----------------------------+
1134 | SMPI_SAMPLE() macro | Only once per loop nest | Always |
1135 +------------------------------------+-------------------------+-----------------------------+
1137 .. _cfg=smpi/comp-adjustment-file:
1139 Slow-down or speed-up parts of your code
1140 ........................................
1142 **Option** ``smpi/comp-adjustment-file:`` **Default:** unset
1144 This option allows you to pass a file that contains two columns: The
1145 first column defines the section that will be subject to a speedup;
1146 the second column is the speedup. For instance:
1148 .. code-block:: none
1150 "start:stop","ratio"
1151 "exchange_1.f:30:exchange_1.f:130",1.18244559422142
1153 The first line is the header - you must include it. The following
1154 line means that the code between two consecutive MPI calls on line 30
1155 in exchange_1.f and line 130 in exchange_1.f should receive a speedup
1156 of 1.18244559422142. The value for the second column is therefore a
1157 speedup, if it is larger than 1 and a slowdown if it is smaller
1158 than 1. Nothing will be changed if it is equal to 1.
1160 Of course, you can set any arbitrary filenames you want (so the start
1161 and end don't have to be in the same file), but be aware that this
1162 mechanism only supports `consecutive calls!`
1164 Please note that you must pass the ``-trace-call-location`` flag to
1165 smpicc or smpiff, respectively. This flag activates some internal
1166 macro definitions that help with obtaining the call location.
1168 Bandwidth and latency factors
1169 .............................
1171 Adapting the bandwidth and latency acurately to the network conditions is of a paramount importance to get realistic results.
1172 This is done through the :ref:`network/bandwidth-factor <cfg=network/bandwidth-factor>` and :ref:`network/latency-factor
1173 <cfg=network/latency-factor>` items. You probably also want to read the following section: :ref:`models_calibration`.
1175 .. _cfg=smpi/display-timing:
1177 Reporting Simulation Time
1178 .........................
1180 **Option** ``smpi/display-timing`` **Default:** 0 (false)
1182 Most of the time, you run MPI code with SMPI to compute the time it
1183 would take to run it on a platform. But since the code is run through
1184 the ``smpirun`` script, you don't have any control on the launcher
1185 code, making it difficult to report the simulated time when the
1186 simulation ends. If you enable the ``smpi/display-timing`` item,
1187 ``smpirun`` will display this information when the simulation
1189 SMPI will also display information about the amout of real time spent
1190 in application code and in SMPI internals, to provide hints about the
1191 need to use sampling to reduce simulation time.
1193 .. _cfg=smpi/display-allocs:
1195 Reporting memory allocations
1196 ............................
1198 **Option** ``smpi/display-allocs`` **Default:** 0 (false)
1200 SMPI intercepts malloc and calloc calls performed inside the running
1201 application, if it wasn't compiled with SMPI_NO_OVERRIDE_MALLOC.
1202 With this option, SMPI will show at the end of execution the amount of
1203 memory allocated through these calls, and locate the most expensive one.
1204 This helps finding the targets for manual memory sharing, or the threshold
1205 to use for smpi/auto-shared-malloc-thresh option (see :ref:`cfg=smpi/auto-shared-malloc-thresh`).
1207 .. _cfg=smpi/keep-temps:
1209 Keeping temporary files after simulation
1210 ........................................
1212 **Option** ``smpi/keep-temps`` **default:** 0 (false)
1214 SMPI usually generates a lot of temporary files that are cleaned after
1215 use. This option requests to preserve them, for example to debug or
1216 profile your code. Indeed, the binary files are removed very early
1217 under the dlopen privatization schema, which tends to fool the
1220 .. _cfg=smpi/papi-events:
1222 Trace hardware counters with PAPI
1223 .................................
1225 **Option** ``smpi/papi-events`` **default:** unset
1227 When the PAPI support is compiled into SimGrid, this option takes the
1228 names of PAPI counters and adds their respective values to the trace
1229 files (See Section :ref:`tracing_tracing_options`).
1233 This feature currently requires superuser privileges, as registers
1234 are queried. Only use this feature with code you trust! Call
1235 smpirun for instance via ``smpirun -wrapper "sudo "
1236 <your-parameters>`` or run ``sudo sh -c "echo 0 >
1237 /proc/sys/kernel/perf_event_paranoid"`` In the later case, sudo
1238 will not be required.
1240 It is planned to make this feature available on a per-process (or per-thread?) basis.
1241 The first draft, however, just implements a "global" (i.e., for all processes) set
1242 of counters, the "default" set.
1244 .. code-block:: none
1246 --cfg=smpi/papi-events:"default:PAPI_L3_LDM:PAPI_L2_LDM"
1248 .. _cfg=smpi/privatization:
1250 Automatic Privatization of Global Variables
1251 ...........................................
1253 **Option** ``smpi/privatization`` **default:** "dlopen" (when using smpirun)
1255 MPI executables are usually meant to be executed in separate
1256 processes, but SMPI is executed in only one process. Global variables
1257 from executables will be placed in the same memory region and shared
1258 between processes, causing intricate bugs. Several options are
1259 possible to avoid this, as described in the main `SMPI publication
1260 <https://hal.inria.fr/hal-01415484>`_ and in the :ref:`SMPI
1261 documentation <SMPI_what_globals>`. SimGrid provides two ways of
1262 automatically privatizing the globals, and this option allows one to
1263 choose between them.
1265 - **no** (default when not using smpirun): Do not automatically
1266 privatize variables. Pass ``-no-privatize`` to smpirun to disable
1268 - **dlopen** or **yes** (default when using smpirun): Link multiple
1269 times against the binary.
1270 - **mmap** (slower, but maybe somewhat more stable):
1271 Runtime automatic switching of the data segments.
1274 This configuration option cannot be set in your platform file. You can only
1275 pass it as an argument to smpirun.
1277 .. _cfg=smpi/privatize-libs:
1279 Automatic privatization of global variables inside external libraries
1280 .....................................................................
1282 **Option** ``smpi/privatize-libs`` **default:** unset
1284 **Linux/BSD only:** When using dlopen (default) privatization,
1285 privatize specific shared libraries with internal global variables, if
1286 they can't be linked statically. For example libgfortran is usually
1287 used for Fortran I/O and indexes in files can be mixed up.
1289 Multiple libraries can be given, semicolon separated.
1291 This configuration option can only use either full paths to libraries,
1292 or full names. Check with ldd the name of the library you want to
1295 .. code-block:: console
1299 libgfortran.so.3 => /usr/lib/x86_64-linux-gnu/libgfortran.so.3 (0x00007fbb4d91b000)
1302 Then you can use ``--cfg=smpi/privatize-libs:libgfortran.so.3``
1303 or ``--cfg=smpi/privatize-libs:/usr/lib/x86_64-linux-gnu/libgfortran.so.3``,
1304 but not ``libgfortran`` nor ``libgfortran.so``.
1306 .. _cfg=smpi/send-is-detached-thresh:
1308 Simulating MPI detached send
1309 ............................
1311 **Option** ``smpi/send-is-detached-thresh`` **default:** 65536
1313 This threshold specifies the size in bytes under which the send will
1314 return immediately. This is different from the threshold detailed in
1315 :ref:`cfg=smpi/async-small-thresh` because the message is not
1316 really sent when the send is posted. SMPI still waits for the
1317 corresponding receive to be posted, in order to perform the communication
1320 .. _cfg=smpi/coll-selector:
1322 Simulating MPI collective algorithms
1323 ....................................
1325 **Option** ``smpi/coll-selector`` **Possible values:** naive (default), ompi, mpich
1327 SMPI implements more than 100 different algorithms for MPI collective
1328 communication, to accurately simulate the behavior of most of the
1329 existing MPI libraries. The ``smpi/coll-selector`` item can be used to
1330 select the decision logic either of the OpenMPI or the MPICH libraries. (By
1331 default SMPI uses naive version of collective operations.)
1333 Each collective operation can be manually selected with a
1334 ``smpi/collective_name:algo_name``. Available algorithms are listed in
1335 :ref:`SMPI_use_colls`.
1337 .. TODO:: All available collective algorithms will be made available
1338 via the ``smpirun --help-coll`` command.
1340 .. _cfg=smpi/barrier-collectives:
1342 Add a barrier in all collectives
1343 ................................
1345 **Option** ``smpi/barrier-collectives`` **default:** off
1347 This option adds a simple barrier in some collective operations to catch dangerous
1348 code that may or may not work depending on the MPI implementation: Bcast, Exscan,
1349 Gather, Gatherv, Scan, Scatter, Scatterv and Reduce.
1351 For example, the following code works with OpenMPI while it deadlocks in MPICH and
1352 Intel MPI. Broadcast seem to be "fire and forget" in OpenMPI while other
1353 implementations expect to receive a message.
1358 MPI_Bcast(buf1, buff_size, MPI_CHAR, 0, newcom);
1359 MPI_Send(&buf2, buff_size, MPI_CHAR, 1, tag, newcom);
1360 } else if (rank==1) {
1361 MPI_Recv(&buf2, buff_size, MPI_CHAR, 0, tag, newcom, MPI_STATUS_IGNORE);
1362 MPI_Bcast(buf1, buff_size, MPI_CHAR, 0, newcom);
1365 The barrier is only simulated and does not involve any additional message (it is a S4U barrier).
1366 This option is disabled by default, and activated by the `-analyze` flag of smpirun.
1368 .. _cfg=smpi/barrier-finalization:
1370 Add a barrier in MPI_Finalize
1371 .............................
1373 **Option** ``smpi/finalization-barrier`` **default:** off
1375 By default, SMPI processes are destroyed as soon as soon as their code ends,
1376 so after a successful MPI_Finalize call returns. In some rare cases, some data
1377 might have been attached to MPI objects still active in the remaining processes,
1378 and can be destroyed eagerly by the finished process.
1379 If your code shows issues at finalization, such as segmentation fault, triggering
1380 this option will add an explicit MPI_Barrier(MPI_COMM_WORLD) call inside the
1381 MPI_Finalize, so that all processes will terminate at almost the same point.
1382 It might affect the total timing by the cost of a barrier.
1384 .. _cfg=smpi/errors-are-fatal:
1386 Disable MPI fatal errors
1387 ........................
1389 **Option** ``smpi/errors-are-fatal`` **default:** on
1391 By default, SMPI processes will crash if a MPI error code is returned. MPI allows
1392 to explicitely set MPI_ERRORS_RETURN errhandler to avoid this behaviour. This flag
1393 will turn on this behaviour by default (for all concerned types and errhandlers).
1394 This can ease debugging by going after the first reported error.
1396 .. _cfg=smpi/pedantic:
1398 Disable pedantic MPI errors
1399 ...........................
1401 **Option** ``smpi/pedantic`` **default:** on
1403 By default, SMPI will report all errors it finds in MPI codes. Some of these errors
1404 may not be considered as errors by all developers. This flag can be turned off to
1405 avoid reporting some usually harmless mistakes.
1406 Concerned errors list (will be expanded in the future):
1408 - Calling MPI_Win_fence only once in a program, hence just opening an epoch without
1411 .. _cfg=smpi/iprobe:
1413 Inject constant times for MPI_Iprobe
1414 ....................................
1416 **Option** ``smpi/iprobe`` **default:** 0.0001
1418 The behavior and motivation for this configuration option is identical
1419 with :ref:`smpi/test <cfg=smpi/test>`, but for the function
1422 .. _cfg=smpi/iprobe-cpu-usage:
1424 Reduce speed for iprobe calls
1425 .............................
1427 **Option** ``smpi/iprobe-cpu-usage`` **default:** 1 (no change)
1429 MPI_Iprobe calls can be heavily used in applications. To account
1430 correctly for the energy that cores spend probing, it is necessary to
1431 reduce the load that these calls cause inside SimGrid.
1433 For instance, we measured a maximum power consumption of 220 W for a
1434 particular application but only 180 W while this application was
1435 probing. Hence, the correct factor that should be passed to this
1436 option would be 180/220 = 0.81.
1440 Inject constant times for MPI_Init
1441 ..................................
1443 **Option** ``smpi/init`` **default:** 0
1445 The behavior and motivation for this configuration option is identical
1446 with :ref:`smpi/test <cfg=smpi/test>`, but for the function ``MPI_Init()``.
1450 Inject constant times for MPI_Isend()
1451 .....................................
1453 **Option** ``smpi/ois``
1455 The behavior and motivation for this configuration option is identical
1456 with :ref:`smpi/os <cfg=smpi/os>`, but for the function ``MPI_Isend()``.
1460 Inject constant times for MPI_send()
1461 ....................................
1463 **Option** ``smpi/os``
1465 In several network models such as LogP, send (MPI_Send, MPI_Isend) and
1466 receive (MPI_Recv) operations incur costs (i.e., they consume CPU
1467 time). SMPI can factor these costs in as well, but the user has to
1468 configure SMPI accordingly as these values may vary by machine. This
1469 can be done by using ``smpi/os`` for MPI_Send operations; for MPI_Isend
1470 and MPI_Recv, use ``smpi/ois`` and ``smpi/or``, respectively. These work
1471 exactly as ``smpi/ois``.
1473 This item can consist of multiple sections; each section takes three
1474 values, for example ``1:3:2;10:5:1``. The sections are divided by ";"
1475 so this example contains two sections. Furthermore, each section
1476 consists of three values.
1478 1. The first value denotes the minimum size in bytes for this section to take effect;
1479 read it as "if message size is greater than this value (and other section has a larger
1480 first value that is also smaller than the message size), use this".
1481 In the first section above, this value is "1".
1483 2. The second value is the startup time; this is a constant value that will always
1484 be charged, no matter what the size of the message. In the first section above,
1487 3. The third value is the `per-byte` cost. That is, it is charged for every
1488 byte of the message (incurring cost messageSize*cost_per_byte)
1489 and hence accounts also for larger messages. In the first
1490 section of the example above, this value is "2".
1492 Now, SMPI always checks which section it should use for a given
1493 message; that is, if a message of size 11 is sent with the
1494 configuration of the example above, only the second section will be
1495 used, not the first, as the first value of the second section is
1496 closer to the message size. Hence, when ``smpi/os=1:3:2;10:5:1``, a
1497 message of size 11 incurs the following cost inside MPI_Send:
1498 ``5+11*1`` because 5 is the startup cost and 1 is the cost per byte.
1500 Note that the order of sections can be arbitrary; they will be ordered internally.
1504 Inject constant times for MPI_Recv()
1505 ....................................
1507 **Option** ``smpi/or``
1509 The behavior and motivation for this configuration option is identical
1510 with :ref:`smpi/os <cfg=smpi/os>`, but for the function ``MPI_Recv()``.
1513 .. _cfg=smpi/grow-injected-times:
1515 Inject constant times for MPI_Test
1516 ..................................
1518 **Option** ``smpi/test`` **default:** 0.0001
1520 By setting this option, you can control the amount of time a process
1521 sleeps when MPI_Test() is called; this is important, because SimGrid
1522 normally only advances the time while communication is happening and
1523 thus, MPI_Test will not add to the time, resulting in deadlock if it is
1524 used as a break-condition as in the following example:
1529 MPI_Test(request, flag, status);
1533 To speed up execution, we use a counter to keep track of how often we
1534 checked if the handle is now valid or not. Hence, we actually
1535 use counter*SLEEP_TIME, that is, the time MPI_Test() causes the
1536 process to sleep increases linearly with the number of previously
1537 failed tests. This behavior can be disabled by setting
1538 ``smpi/grow-injected-times`` to **no**. This will also disable this
1539 behavior for MPI_Iprobe.
1541 .. _cfg=smpi/shared-malloc:
1542 .. _cfg=smpi/shared-malloc-hugepage:
1547 **Option** ``smpi/shared-malloc`` **Possible values:** global (default), local
1549 If your simulation consumes too much memory, you may want to modify
1550 your code so that the working areas are shared by all MPI ranks. For
1551 example, in a block-cyclic matrix multiplication, you will only
1552 allocate one set of blocks, and all processes will share them.
1553 Naturally, this will lead to very wrong results, but this will save a
1554 lot of memory. So this is still desirable for some studies. For more on
1555 the motivation for that feature, please refer to the `relevant section
1556 <https://simgrid.github.io/SMPI_CourseWare/topic_understanding_performance/matrixmultiplication>`_
1557 of the SMPI CourseWare (see Activity #2.2 of the pointed
1558 assignment). In practice, change the calls for malloc() and free() into
1559 SMPI_SHARED_MALLOC() and SMPI_SHARED_FREE().
1561 SMPI provides two algorithms for this feature. The first one, called
1562 ``local``, allocates one block per call to SMPI_SHARED_MALLOC()
1563 (each call site gets its own block) ,and this block is shared
1564 among all MPI ranks. This is implemented with the shm_* functions
1565 to create a new POSIX shared memory object (kept in RAM, in /dev/shm)
1566 for each shared block.
1568 With the ``global`` algorithm, each call to SMPI_SHARED_MALLOC()
1569 returns a new address, but it only points to a shadow block: its memory
1570 area is mapped on a 1 MiB file on disk. If the returned block is of size
1571 N MiB, then the same file is mapped N times to cover the whole block.
1572 At the end, no matter how many times you call SMPI_SHARED_MALLOC, this will
1573 only consume 1 MiB in memory.
1575 You can disable this behavior and come back to regular mallocs (for
1576 example for debugging purposes) using ``no`` as a value.
1578 If you want to keep private some parts of the buffer, for instance if these
1579 parts are used by the application logic and should not be corrupted, you
1580 can use SMPI_PARTIAL_SHARED_MALLOC(size, offsets, offsets_count). For example:
1584 mem = SMPI_PARTIAL_SHARED_MALLOC(500, {27,42 , 100,200}, 2);
1586 This will allocate 500 bytes to mem, such that mem[27..41] and
1587 mem[100..199] are shared while other area remain private.
1589 Then, it can be deallocated by calling SMPI_SHARED_FREE(mem).
1591 When smpi/shared-malloc:global is used, the memory consumption problem
1592 is solved, but it may induce too much load on the kernel's pages table.
1593 In this case, you should use huge pages so that the kernel creates only one
1594 entry per MB of malloced data instead of one entry per 4 kB.
1595 To activate this, you must mount a hugetlbfs on your system and allocate
1596 at least one huge page:
1598 .. code-block:: console
1601 $ sudo mount none /home/huge -t hugetlbfs -o rw,mode=0777
1602 $ sudo sh -c 'echo 1 > /proc/sys/vm/nr_hugepages' # echo more if you need more
1604 Then, you can pass the option
1605 ``--cfg=smpi/shared-malloc-hugepage:/home/huge`` to smpirun to
1606 actually activate the huge page support in shared mallocs.
1608 .. _cfg=smpi/auto-shared-malloc-thresh:
1610 Automatically share allocations
1611 ...............................
1613 **Option** ``smpi/auto-shared-malloc-thresh:`` **Default:** 0 (false)
1614 This value in bytes represents the size above which all allocations
1615 will be "shared" by default (as if they were performed through
1616 SMPI_SHARED_MALLOC macros). Default = 0 = disabled feature.
1617 The value must be carefully chosen to only select data buffers which
1618 will not modify execution path or cause crash if their content is false.
1619 Option :ref:`cfg=smpi/display-allocs` can be used to locate the largest
1620 allocation detected in a run, and provide a good starting threshold.
1621 Note : malloc, calloc and free are overridden by smpicc/cxx by default.
1622 This can cause some troubles if codes are already overriding these. If this
1623 is the case, defining SMPI_NO_OVERRIDE_MALLOC in the compilation flags can
1624 help, but will make this feature unusable.
1628 Inject constant times for MPI_Wtime, gettimeofday and clock_gettime
1629 ...................................................................
1631 **Option** ``smpi/wtime`` **default:** 10 ns
1633 This option controls the amount of (simulated) time spent in calls to
1634 MPI_Wtime(), gettimeofday() and clock_gettime(). If you set this value
1635 to 0, the simulated clock is not advanced in these calls, which leads
1636 to issues if your application contains such a loop:
1640 while(MPI_Wtime() < some_time_bound) {
1641 /* some tests, with no communication nor computation */
1644 When the option smpi/wtime is set to 0, the time advances only on
1645 communications and computations. So the previous code results in an
1646 infinite loop: the current [simulated] time will never reach
1647 ``some_time_bound``. This infinite loop is avoided when that option
1648 is set to a small value, as it is by default since SimGrid v3.21.
1650 Note that if your application does not contain any loop depending on
1651 the current time only, then setting this option to a non-zero value
1652 will slow down your simulations by a tiny bit: the simulation loop has
1653 to be broken out of and reset each time your code asks for the current time.
1654 If the simulation speed really matters to you, you can avoid this
1655 extra delay by setting smpi/wtime to 0.
1657 .. _cfg=smpi/list-leaks:
1659 Report leaked MPI objects
1660 .........................
1662 **Option** ``smpi/list-leaks`` **default:** 0
1664 This option controls whether to report leaked MPI objects.
1665 The parameter is the number of leaks to report.
1667 Other Configurations
1668 --------------------
1670 .. _cfg=debug/clean-atexit:
1672 Cleanup at Termination
1673 ......................
1675 **Option** ``debug/clean-atexit`` **default:** on
1677 If your code is segfaulting during its finalization, it may help to
1678 disable this option to request that SimGrid not attempt any cleanups at
1679 the end of the simulation. Since the Unix process is ending anyway,
1680 the operating system will wipe it all.
1687 **Option** ``path`` **default:** . (current dir)
1689 It is possible to specify a list of directories to search in for the
1690 trace files (see :ref:`pf_trace`) by using this configuration
1691 item. To add several directory to the path, set the configuration
1692 item several times, as in ``--cfg=path:toto --cfg=path:tutu``
1694 .. _cfg=debug/breakpoint:
1699 **Option** ``debug/breakpoint`` **default:** unset
1701 This configuration option sets a breakpoint: when the simulated clock
1702 reaches the given time, a SIGTRAP is raised. This can be used to stop
1703 the execution and get a backtrace with a debugger.
1705 It is also possible to set the breakpoint from inside the debugger, by
1706 writing in global variable simgrid::kernel::cfg_breakpoint. For example,
1709 .. code-block:: none
1711 set variable simgrid::kernel::cfg_breakpoint = 3.1416
1713 .. _cfg=debug/verbose-exit:
1718 **Option** ``debug/verbose-exit`` **default:** on
1720 By default, when Ctrl-C is pressed, the status of all existing actors
1721 is displayed before exiting the simulation. This is very useful to
1722 debug your code, but it can become troublesome if you have many
1723 actors. Set this configuration item to **off** to disable this
1726 .. _cfg=exception/cutpath:
1728 Truncate local path from exception backtrace
1729 ............................................
1731 **Option** ``exception/cutpath`` **default:** off
1733 This configuration option is used to remove the path from the
1734 backtrace shown when an exception is thrown. This is mainly useful for
1735 the tests: the full file path would makes the tests non-reproducible because
1736 the paths of source files depend of the build settings. That would
1737 break most of the tests since their output is continually compared.
1741 Logging configuration
1742 ---------------------
1744 As introduced in :ref:`outcome_logs`, the SimGrid logging mechanism allows to configure at runtime the messages that should be displayed and those that should be omitted. Each
1745 message produced in the code is given a category (denoting its topic) and a priority. Then at runtime, each category is given a threshold (only messages of priority higher than
1746 that threshold are displayed), a layout (deciding how the messages in this category are formatted), and an appender (deciding what to do with the message: either print on stderr or
1749 This section explains how to configure this logging features. You can also refer to the documentation of the :ref:`programmer's interface <logging_prog>`, that allows to produce
1750 messages from your code.
1752 Most of the time, the logging mechanism is configured at runtime using the ``--log`` command-line argument, even if you can also use :c:func:`xbt_log_control_set()` to control it from
1753 your program. To pass configure more than one setting, you can either pass several ``--log`` arguments, or separate your settings with spaces, that must be quoted accordingly. In
1754 practice, the following is equivalent to the above settings: ``--log=root.thresh:error --log=s4u_host.thresh:debug``.
1756 If you want to specify more than one setting, you can either pass several ``--log`` argument to your program as above, or separate them with spaces. In this case, you want to quote
1757 your settings, as in ``--log="root.thresh:error s4u_host.thresh:debug"``. The parameters are interpreted in order, from left to right.
1760 Threshold configuration
1761 .......................
1763 The keyword ``threshold`` controls which logging event will get displayed in a given category. For example, ``--log=root.threshold:debug`` displays *every* message produced in the
1764 ``root`` category and its subcategories (i.e., every message produced -- this is *extremely* verbose), while ``--log=root.thres:critical`` turns almost everything off. As you can
1765 see, ``threshold`` can be abbreviated here.
1767 Existing thresholds:
1769 - ``trace`` some functions display a message at this level when entering or returning
1770 - ``debug`` output that is mostly useful when debugging the corresponding module.
1771 - ``verbose`` verbose output that is only mildly interesting and can easily be ignored
1772 - ``info`` usual output (this is the default threshold of all categories)
1773 - ``warning`` minor issue encountered
1774 - ``error`` issue encountered
1775 - ``critical`` major issue encountered, such as assertions failures
1779 Format configuration
1780 ....................
1782 The keyword ``fmt`` controls the layout (the format) of a logging category. For example, ``--log=root.fmt:%m`` reduces the output to the user-message only, removing any decoration such
1783 as the date, or the actor ID, everything. Existing format directives:
1786 - %n: line separator (LOG4J compatible)
1787 - %e: plain old space (SimGrid extension)
1789 - %m: user-provided message
1791 - %c: Category name (LOG4J compatible)
1792 - %p: Priority name (LOG4J compatible)
1794 - %h: Hostname (SimGrid extension)
1795 - %a: Actor name (SimGrid extension -- note that with SMPI this is the integer value of the process rank)
1796 - %i: Actor PID (SimGrid extension -- this is a 'i' as in 'i'dea)
1797 - %t: Thread "name" (LOG4J compatible -- actually the address of the thread in memory)
1799 - %F: file name where the log event was raised (LOG4J compatible)
1800 - %l: location where the log event was raised (LOG4J compatible, like '%%F:%%L' -- this is a l as in 'l'etter)
1801 - %L: line number where the log event was raised (LOG4J compatible)
1802 - %M: function name (LOG4J compatible -- called method name here of course).
1804 - %d: date (UNIX-like epoch)
1805 - %r: application age (time elapsed since the beginning of the application)
1808 ``--log=root.fmt:'[%h:%a:(%i) %r] %l: %m%n'`` gives you the default layout used for info messages while ``--log=root.fmt:'[%h:%a:(%i) %r] %l: [%c/%p] %m%n'`` gives you the default
1809 layout for the other priorities (it adds the source code location). Also, the actor identification is omitted by the default layout for the messages coming directly from the
1810 SimGrid kernel, so info messages are formatted with ``[%r] [%c/%p] %m%n`` in this case. When specifying the layout manually, such distinctions are currently impossible, and the
1811 provided layout is used for every messages.
1813 As with printf, you can specify the precision and width of the fields. For example, ``%.4r`` limits the date precision to four digits while ``%15h`` limits the host name to at most
1817 If you want to have spaces in your log format, you should protect it. Otherwise, SimGrid will consider that this is a space-separated list of several parameters. But you should
1818 also protect it from the shell that also splits command line arguments on spaces. At the end, you should use something such as ``--log="'root.fmt:%l: [%p/%c]: %m%n'"``.
1819 Another option is to use the ``%e`` directive for spaces, as in ``--log=root.fmt:%l:%e[%p/%c]:%e%m%n``.
1824 The keyword ``app`` controls the appended of a logging category. For example ``--log=root.app:file:mylogfile`` redirects every output to the file ``mylogfile``.
1826 With the ``splitfile`` appender, a new file is created when the size of the output reaches the specified size. The format is ``--log=root.app:splitfile:<size>:<file name>``. For
1827 example, ``--log=root.app:splitfile:500:mylog_%`` creates log files of at most 500 bytes, using the names ``mylog_0``, ``mylog_1``, ``mylog_2``, etc.
1829 The ``rollfile`` appender uses one file only, but the file is emptied and recreated when its size reaches the specified maximum. For example, ``--log=root.app:rollfile:500:mylog``
1830 ensures that the log file ``mylog`` will never overpass 500 bytes in size.
1832 Any appender setup this way have its own layout format, that you may change afterward. When specifying a new appender, its additivity is set to false to prevent log event displayed
1833 by this appender to "leak" to any other appender higher in the hierarchy. You can naturally change that if you want your messages to be displayed twice.
1838 The keyword ``add`` controls the additivity of a logging category. By default, the messages are only passed one appender only: the more specific, i.e. the first one found when
1839 climbing the tree from the category in which they were produced. In Log4J parlance, it is said that the default additivity of appenders is false. If you change this setting to
1840 ``on`` (or ``yes`` or ``1``), the produced messages will also be passed to the upper appender.
1842 Let's consider a more complex example: ``--log="root.app:file:all.log s4u.app:file:iface.log xbt.app:file:xbt.log xbt.add:yes``. Here, the logging of s4u will be sent to the
1843 ``iface.log`` file; the logging of the xbt toolbox will be sent to both the ``xbt.log`` file and the ``all.log`` file (because xbt additivity was enabled); and every other loggings
1844 will only be sent to ``all.log``.
1849 ``--help-logs`` displays a complete help message about logging in SimGrid.
1851 ``--help-log-categories`` displays the actual hierarchy of log categories for this binary.
1853 ``--log=no_loc`` hides the source locations (file names and line numbers) from the messages. This is useful to make tests reproducible.