Fix tesh with new dependencies on Mutex

[simgrid.git] / docs / source / Tutorial_DAG.rst

diff --git a/docs/source/Tutorial_DAG.rst b/docs/source/Tutorial_DAG.rst
index e807cc4..4bddc09 100644 (file)
--- a/docs/source/Tutorial_DAG.rst
+++ b/docs/source/Tutorial_DAG.rst
@@ -3,7 +3,7 @@
 Simulating DAG
 ==============
 
 Simulating DAG
 ==============
 

-This tutorial presents the basics to understand how DAG are represented in Simgrid and how to simulate their workflow. 
+This tutorial presents the basics to understand how DAG are represented in SimGrid and how to simulate their workflow.

 
 Definition of a DAG
 -------------------
 
 Definition of a DAG
 -------------------


@@ -26,7 +26,7 @@ Set of edges representing precedence constraints between :ref:`Activities <API_s
 
    \mathcal{E} = {e_i,j | (i,j) \in {1, ..., V} x {1, ..., V}}
 
 
    \mathcal{E} = {e_i,j | (i,j) \in {1, ..., V} x {1, ..., V}}
 

-.. image:: /tuto_dag/img/dag.svg
+.. image:: /img/dag.svg

    :align: center
 
 Representing Vertices/Activities
    :align: center
 
 Representing Vertices/Activities


@@ -58,7 +58,7 @@ Representing Edges/Dependencies
 
 An activity will not start until all of its dependencies have been completed.
 Activities may have any number of successors.
 
 An activity will not start until all of its dependencies have been completed.
 Activities may have any number of successors.

-Dependencies between Activities are created using :cpp:func:`Activity::add_successor(ActivityPtr)`.
+Dependencies between Activities are created using :cpp:func:`simgrid::s4u::Activity::add_successor`.

 
 .. code-block:: cpp
 
 
 .. code-block:: cpp
 


@@ -71,118 +71,92 @@ Lab 1: Basics
 
 The goal of this lab is to describe the following DAG: 
 
 
 The goal of this lab is to describe the following DAG: 
 

-.. image:: /tuto_dag/img/dag1.svg
+.. image:: /img/dag1.svg

    :align: center
 
 In this DAG we want ``c1`` to compute 1e9 flops, ``c2`` to compute 5e9 flops and ``c3`` to compute 2e9 flops. 
 There is also a data transfer of 5e8 bytes between ``c1`` and ``c3``.
 
    :align: center
 
 In this DAG we want ``c1`` to compute 1e9 flops, ``c2`` to compute 5e9 flops and ``c3`` to compute 2e9 flops. 
 There is also a data transfer of 5e8 bytes between ``c1`` and ``c3``.
 

-First of all, include the Simgrid library and define the log category.
+First of all, include the SimGrid library and define the log category.

 
 

-.. code-block:: cpp
-
-   #include "simgrid/s4u.hpp"
-
-   XBT_LOG_NEW_DEFAULT_CATEGORY(main, "Messages specific for this s4u tutorial");
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 6-8

 
 Inside the ``main`` function create an instance of :ref:`Engine <API_s4u_Engine>` and load the platform.
 
 
 Inside the ``main`` function create an instance of :ref:`Engine <API_s4u_Engine>` and load the platform.
 

-.. code-block:: cpp
-
-    simgrid::s4u::Engine e(&argc, argv);
-    e.load_platform(argv[1]);
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 12-13

 
 Retrieve pointers to some hosts.
 
 
 Retrieve pointers to some hosts.
 

-.. code-block:: cpp
-
-    simgrid::s4u::Host* tremblay = e.host_by_name("Tremblay");
-    simgrid::s4u::Host* jupiter  = e.host_by_name("Jupiter");
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 15-16

 
 Initiate the activities.
 
 
 Initiate the activities.
 

-.. code-block:: cpp
-
-    simgrid::s4u::ExecPtr c1 = simgrid::s4u::Exec::init();
-    simgrid::s4u::ExecPtr c2 = simgrid::s4u::Exec::init();
-    simgrid::s4u::ExecPtr c3 = simgrid::s4u::Exec::init();
-    simgrid::s4u::CommPtr t1 = simgrid::s4u::Comm::sendto_init();
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 18-21

 
 Give names to thoses activities.
 
 
 Give names to thoses activities.
 

-.. code-block:: cpp
-
-    c1->set_name("c1");
-    c2->set_name("c2");
-    c3->set_name("c3");
-    t1->set_name("t1");
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 23-26

 
 Set the amount of work for each activity.
 
 
 Set the amount of work for each activity.
 

-.. code-block:: cpp
-
-    c1->set_flops_amount(1e9);
-    c2->set_flops_amount(5e9);
-    c3->set_flops_amount(2e9);
-    t1->set_payload_size(5e8);
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 28-31

 
 Define the dependencies between the activities.
 
 
 Define the dependencies between the activities.
 

-.. code-block:: cpp
-
-    c1->add_successor(t1);
-    t1->add_successor(c3);
-    c2->add_successor(c3);
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 33-35

 
 Set the location of each Exec activity and source and destination for the Comm activity.
 
 
 Set the location of each Exec activity and source and destination for the Comm activity.
 

-.. code-block:: cpp
-
-    c1->set_host(tremblay);
-    c2->set_host(jupiter);
-    c3->set_host(jupiter);
-    t1->set_source(tremblay);
-    t1->set_destination(jupiter);
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 37-41

 
 Start the executions of Activities without dependencies.
 
 
 Start the executions of Activities without dependencies.
 

-.. code-block:: cpp
-
-    c1->start();
-    c2->start();
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 43-44

 
 Add a callback to monitor the activities.
 
 
 Add a callback to monitor the activities.
 

-.. code-block:: cpp
-
-   Activity::on_completion_cb([](simgrid::s4u::Activity const& activity) {
-      XBT_INFO("Activity '%s' is complete (start time: %f, finish time: %f)", activity.get_cname(), activity.get_start_time(),
-               activity.get_finish_time());
-      });
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 46-49

 
 Finally, run the simulation.
 
 
 Finally, run the simulation.
 

-.. code-block:: cpp
-
-   e.run();
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.cpp
+   :language: cpp
+   :lines: 51

 
 The execution of this code should give you the following output:
 
 
 The execution of this code should give you the following output:
 

-.. code-block:: bash
-
-   [10.194200] [main/INFO] Activity 'c1' is complete (start time: 0.000000, finish time: 10.194200)
-   [65.534235] [main/INFO] Activity 'c2' is complete (start time: 0.000000, finish time: 65.534235)
-   [85.283378] [main/INFO] Activity 't1' is complete (start time: 10.194200, finish time: 85.283378)
-   [111.497072] [main/INFO] Activity 'c3' is complete (start time: 85.283378, finish time: 111.497072)
+.. literalinclude:: ../../examples/cpp/dag-tuto/s4u-dag-tuto.tesh
+   :language: none
+   :lines: 4-

 
 Lab 2: Import a DAG from a file
 
 Lab 2: Import a DAG from a file

----------------
+-------------------------------

 
 

-In this lab we present how to import a DAG into you Simgrid simulation, either using a DOT file, a JSON file, or a DAX file. 
+In this lab we present how to import a DAG into you SimGrid simulation, either using a DOT file, a JSON file, or a DAX file.

 
 The files presented in this lab describe the following DAG:
 
 
 The files presented in this lab describe the following DAG:
 

-.. image:: /tuto_dag/img/dag2.svg
+.. image:: /img/dag2.svg

    :align: center
 
 From a DOT file
    :align: center
 
 From a DOT file


@@ -192,227 +166,245 @@ A DOT file describes a workflow in accordance with the graphviz format.
 
 The following DOT file describes the workflow presented at the beginning of this lab:
 
 
 The following DOT file describes the workflow presented at the beginning of this lab:
 

-.. code-block:: xml
+.. literalinclude:: ../../examples/cpp/dag-from-dot-simple/dag.dot
+   :language: dot

 
 

-   digraph G {
-      c1 [size="1e9"];
-      c2 [size="5e9"];
-      c3 [size="2e9"];
+It can be imported as a vector of Activities into SimGrid using :cpp:func:`simgrid::s4u::create_DAG_from_DOT`. Then, you have to assign hosts to your Activities.

 
 

-      root->c1 [size="2e8"];
-      root->c2 [size="1e8"];
-      c1->c3   [size="5e8"];
-      c2->c3   [size="-1"];
-      c3->end  [size="2e8"];
-   }
+.. literalinclude:: ../../examples/cpp/dag-from-dot-simple/s4u-dag-from-dot-simple.cpp
+   :language: cpp

 
 

-It can be imported as a vector of Activities into Simgrid using :cpp:func:`create_DAG_from_DOT(const std::string& filename)`. Then, you have to assign hosts to your Activities.
+The execution of this code should give you the following output:

 
 

-.. code-block:: cpp
+.. literalinclude:: ../../examples/cpp/dag-from-dot-simple/s4u-dag-from-dot-simple.tesh
+   :language: none
+   :lines: 4-

 
 

-   #include "simgrid/s4u.hpp"
+From a JSON file
+................

 
 

-   XBT_LOG_NEW_DEFAULT_CATEGORY(main, "Messages specific for this s4u example");
+A JSON file describes a workflow in accordance with the `wfformat <https://github.com/wfcommons/wfformat>`_ .

 
 

-   int main(int argc, char* argv[]) {
-      simgrid::s4u::Engine e(&argc, argv);
-      e.load_platform(argv[1]);
+The following JSON file describes the workflow presented at the beginning of this lab:

 
 

-      std::vector<simgrid::s4u::ActivityPtr> dag = simgrid::s4u::create_DAG_from_dot(argv[2]);
+.. literalinclude:: ../../examples/cpp/dag-from-json-simple/dag.json
+   :language: json

 
 

-      simgrid::s4u::Host* tremblay = e.host_by_name("Tremblay");
-      simgrid::s4u::Host* jupiter  = e.host_by_name("Jupiter");
-      simgrid::s4u::Host* fafard  = e.host_by_name("Fafard");
+It can be imported as a vector of Activities into SimGrid using :cpp:func:`simgrid::s4u::create_DAG_from_json`.

 
 

-      dynamic_cast<simgrid::s4u::Exec*>(dag[0].get())->set_host(fafard);
-      dynamic_cast<simgrid::s4u::Exec*>(dag[1].get())->set_host(tremblay);
-      dynamic_cast<simgrid::s4u::Exec*>(dag[2].get())->set_host(jupiter);
-      dynamic_cast<simgrid::s4u::Exec*>(dag[3].get())->set_host(jupiter);
-      dynamic_cast<simgrid::s4u::Exec*>(dag[8].get())->set_host(jupiter);
-    
-      for (const auto& a : dag) {
-         if (auto* comm = dynamic_cast<simgrid::s4u::Comm*>(a.get())) {
-               auto pred = dynamic_cast<simgrid::s4u::Exec*>((*comm->get_dependencies().begin()).get());
-               auto succ = dynamic_cast<simgrid::s4u::Exec*>(comm->get_successors().front().get());
-               comm->set_source(pred->get_host())->set_destination(succ->get_host());
-         }
-      }
+.. literalinclude:: ../../examples/cpp/dag-from-json-simple/s4u-dag-from-json-simple.cpp
+   :language: cpp

 
 

-      simgrid::s4u::Activity::on_completion_cb([](simgrid::s4u::Activity const& activity) {
-      XBT_INFO("Activity '%s' is complete (start time: %f, finish time: %f)", activity.get_cname(), activity.get_start_time(),
-             activity.get_finish_time());
-      });
+The execution of this code should give you the following output:

 
 

-      e.run();
-      return 0;
-   }
+.. literalinclude:: ../../examples/cpp/dag-from-json-simple/s4u-dag-from-json-simple.tesh
+   :language: none
+   :lines: 4-

 
 

-The execution of this code should give you the following output:
+From a DAX file [deprecated]
+............................

 
 

-.. code-block:: bash
+A DAX file describes a workflow in accordance with the `Pegasus <http://pegasus.isi.edu/>`_ format.

 
 

-   [0.000000] [main/INFO] Activity 'root' is complete (start time: 0.000000, finish time: 0.000000)
-   [33.394394] [main/INFO] Activity 'root->c2' is complete (start time: 0.000000, finish time: 33.394394)
-   [39.832311] [main/INFO] Activity 'root->c1' is complete (start time: 0.000000, finish time: 39.832311)
-   [50.026511] [main/INFO] Activity 'c1' is complete (start time: 39.832311, finish time: 50.026511)
-   [98.928629] [main/INFO] Activity 'c2' is complete (start time: 33.394394, finish time: 98.928629)
-   [125.115689] [main/INFO] Activity 'c1->c3' is complete (start time: 50.026511, finish time: 125.115689)
-   [151.329383] [main/INFO] Activity 'c3' is complete (start time: 125.115689, finish time: 151.329383)
-   [151.743605] [main/INFO] Activity 'c3->end' is complete (start time: 151.329383, finish time: 151.743605)
-   [151.743605] [main/INFO] Activity 'end' is complete (start time: 151.743605, finish time: 151.743605)
+The following DAX file describes the workflow presented at the beginning of this lab:

 
 

-From a JSON file
-................
+.. literalinclude:: ../../examples/cpp/dag-from-dax-simple/dag.xml
+   :language: xml

 
 

-A JSON file describes a workflow in accordance with the `wfformat <https://github.com/wfcommons/wfformat>`_ .
+It can be imported as a vector of Activities into SimGrid using :cpp:func:`simgrid::s4u::create_DAG_from_DAX`.

 
 

-The following JSON file describes the workflow presented at the beginning of this lab:
+.. literalinclude:: ../../examples/cpp/dag-from-dax-simple/s4u-dag-from-dax-simple.cpp
+   :language: cpp

 
 

-.. code-block:: JSON
+Lab 3: Scheduling with the Min-Min algorithm
+--------------------------------------------

 
 

-   {
-      "name": "simple_json",
-      "schemaVersion": "1.0",
-      "workflow": {
-         "makespan": 0,
-         "executedAt": "2023-03-09T00:00:00-00:00",
-         "tasks": [
-         {
-            "name": "c1",
-            "type": "compute",
-            "parents": [],
-            "runtime": 1e9,
-            "machine": "Tremblay"
-         },
-         {
-            "name": "t1",
-            "type": "transfer",
-            "parents": ["c1"],
-            "bytesWritten": 5e8,
-            "machine": "Jupiter"
-         },
-         {
-            "name": "c2",
-            "type": "compute",
-            "parents": [],
-            "runtime": 5e9,
-            "machine": "Jupiter"
-         },
-         {
-            "name": "c3",
-            "type": "compute",
-            "parents": ["t1","c2"],
-         "runtime": 2e9,
-         "machine": "Jupiter"
-         }
-         ],
-         "machines": [
-            {"nodeName": "Tremblay"},
-            {"nodeName": "Jupiter"}
-         ]
-      }
-   }
+In this lab we present how to schedule activities imported from a DAX file using the 
+`Min-Min algorithm <https://www.researchgate.net/figure/The-Traditional-Min-Min-Scheduling-Algorithm_fig5_236346423>`_.
+
+The source code for this lab can be found `here <https://framagit.org/simgrid/simgrid/-/blob/stable/examples/cpp/dag-scheduling/s4u-dag-scheduling.cpp>`_.

 
 

-It can be imported as a vector of Activities into Simgrid using :cpp:func:`create_DAG_from_json(const std::string& filename)`. 
+For code readability we first create the `sg4` namespace.

 
 .. code-block:: cpp
 
 
 .. code-block:: cpp
 

-   #include "simgrid/s4u.hpp"
+   namespace sg4 = simgrid::s4u;

 
 

-   XBT_LOG_NEW_DEFAULT_CATEGORY(main, "Messages specific for this s4u example");
+The core mechanism of the algorithm lies in three functions. 
+They respectively serve the purpose of finding tasks to schedule, 
+finding the best host to execute them and properly scheduling them.

 
 

-   int main(int argc, char* argv[]) {
-      simgrid::s4u::Engine e(&argc, argv);
-      e.load_platform(argv[1]);
+Find Tasks to Schedule
+......................

 
 

-      std::vector<simgrid::s4u::ActivityPtr> dag = simgrid::s4u::create_DAG_from_json(argv[2]);
+The role of this function is to retrieve tasks that are ready to be scheduled, i.e, that have their dependencies solved.

 
 

-      simgrid::s4u::Activity::on_completion_cb([](simgrid::s4u::Activity const& activity) {
-      XBT_INFO("Activity '%s' is complete (start time: %f, finish time: %f)", activity.get_cname(), activity.get_start_time(),
-             activity.get_finish_time());
-      });
+.. literalinclude:: ../../examples/cpp/dag-scheduling/s4u-dag-scheduling.cpp
+   :language: cpp
+   :lines: 15-38

 
 

-      e.run();
-      return 0;
-   }
+Find the Best Placement
+.......................

 
 

-The execution of this code should give you the following output:
+Once we have a task ready to be scheduled, we need to find the best placement for it.
+This is done by evaluating the earliest finish time among all hosts.
+It depends on the duration of the data transfers of the parents of this task to this host.

 
 

-.. code-block:: bash
+.. literalinclude:: ../../examples/cpp/dag-scheduling/s4u-dag-scheduling.cpp
+   :language: cpp
+   :lines: 40-91

 
 

-   [10.194200] [main/INFO] Activity 'c1' is complete (start time: 0.000000, finish time: 10.194200)
-   [65.534235] [main/INFO] Activity 'c2' is complete (start time: 0.000000, finish time: 65.534235)
-   [85.283378] [main/INFO] Activity 't1' is complete (start time: 10.194200, finish time: 85.283378)
-   [111.497072] [main/INFO] Activity 'c3' is complete (start time: 85.283378, finish time: 111.497072)
+Schedule a Task
+...............

 
 

-From a DAX file [deprecated]
-............................
+When the best host has been found, the task is scheduled on it:

 
 

-A DAX file describes a workflow in accordance with the `Pegasus <http://pegasus.isi.edu/>`_ format.
+* it sets the host of the task to schedule
+* it stores the finish time of this task on the host
+* it sets the destination of parents communication
+* it sets the source of any child communication.

 
 

-The following DAX file describes the workflow presented at the beginning of this lab:
+.. literalinclude:: ../../examples/cpp/dag-scheduling/s4u-dag-scheduling.cpp
+   :language: cpp
+   :lines: 93-113
+
+Mixing it all Together
+......................

 
 

-.. code-block:: xml
-
-   <?xml version="1.0" encoding="UTF-8"?>
-   <adag xmlns="http://pegasus.isi.edu/schema/DAX" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-      xsi:schemaLocation="http://pegasus.isi.edu/schema/DAX http://pegasus.isi.edu/schema/dax-2.1.xsd"
-      version="2.1">
-      <job id="1" name="c1" runtime="10">
-         <uses file="i1" link="input" register="true" transfer="true" optional="false" type="data" size="2e8"/>
-         <uses file="o1" link="output" register="true" transfer="true" optional="false" type="data" size="5e8"/>
-      </job>
-      <job id="2" name="c2" runtime="50">
-         <uses file="i2" link="input" register="true" transfer="true" optional="false" type="data" size="1e8"/>
-      </job>
-      <job id="3" name="c3" runtime="20">
-         <uses file="o1" link="input" register="true" transfer="true" optional="false" type="data" size="5e8"/>
-         <uses file="o3" link="output" register="true" transfer="true" optional="false" type="data" size="2e8"/>
-      </job>
-      <child ref="3">
-         <parent ref="1"/>
-         <parent ref="2"/>
-      </child>
-   </adag>
-
-It can be imported as a vector of Activities into Simgrid using :cpp:func:`create_DAG_from_DAX(std::string)`.
+Now that we have the key components of the algorithm let's merge them inside the main function.

 
 .. code-block:: cpp
 
 
 .. code-block:: cpp
 

-   #include "simgrid/s4u.hpp"
+   int main(int argc, char** argv)
+   {
+   ...
+
+First, we initialize the SimGrid Engine.

 
 

-   XBT_LOG_NEW_DEFAULT_CATEGORY(main, "Messages specific for this s4u example");
+.. code-block:: cpp

 
 

-   int main(int argc, char* argv[]) {
-      simgrid::s4u::Engine e(&argc, argv);
-      e.load_platform(argv[1]);
+   sg4::Engine e(&argc, argv);

 
 

-      std::vector<simgrid::s4u::ActivityPtr> dag = simgrid::s4u::create_DAG_from_DAX(argv[2]);
+The Min-Min algorithm schedules unscheduled tasks. 
+To keep track of them we make use of the method :cpp:func:`simgrid::s4u::Engine::track_vetoed_activities`.

 
 

-      simgrid::s4u::Host* tremblay = e.host_by_name("Tremblay");
-      simgrid::s4u::Host* jupiter  = e.host_by_name("Jupiter");
-      simgrid::s4u::Host* fafard  = e.host_by_name("Fafard");
+.. code-block:: cpp

 
 

-      dynamic_cast<simgrid::s4u::Exec*>(dag[0].get())->set_host(fafard);
-      dynamic_cast<simgrid::s4u::Exec*>(dag[1].get())->set_host(tremblay);
-      dynamic_cast<simgrid::s4u::Exec*>(dag[2].get())->set_host(jupiter);
-      dynamic_cast<simgrid::s4u::Exec*>(dag[3].get())->set_host(jupiter);
-      dynamic_cast<simgrid::s4u::Exec*>(dag[8].get())->set_host(jupiter);
-    
-      for (const auto& a : dag) {
-         if (auto* comm = dynamic_cast<simgrid::s4u::Comm*>(a.get())) {
-            auto pred = dynamic_cast<simgrid::s4u::Exec*>((*comm->get_dependencies().begin()).get());
-            auto succ = dynamic_cast<simgrid::s4u::Exec*>(comm->get_successors().front().get());
-            comm->set_source(pred->get_host())->set_destination(succ->get_host());
-         }
+   std::set<sg4::Activity*> vetoed;
+   e.track_vetoed_activities(&vetoed);
+
+We add the following callback that will be triggered at the end of execution activities.
+This callback stores the finish time of the execution, 
+to use it as a start time for any subsequent communications.
+
+.. code-block:: cpp
+
+  sg4::Activity::on_completion_cb([](sg4::Activity const& activity) {
+    // when an Exec completes, we need to set the potential start time of all its ouput comms
+    const auto* exec = dynamic_cast<sg4::Exec const*>(&activity);
+    if (exec == nullptr) // Only Execs are concerned here
+      return;
+    for (const auto& succ : exec->get_successors()) {
+      auto* comm = dynamic_cast<sg4::Comm*>(succ.get());
+      if (comm != nullptr) {
+        auto* finish_time = new double(exec->get_finish_time());
+        // We use the user data field to store the finish time of the predecessor of the comm, i.e., its potential start
+        // time
+        comm->set_data(finish_time);

       }
       }

+    }
+  });
+
+We load the platform and force sequential execution on hosts.

 
 

-      simgrid::s4u::Activity::on_completion_cb([](simgrid::s4u::Activity const& activity) {
-      XBT_INFO("Activity '%s' is complete (start time: %f, finish time: %f)", activity.get_cname(), activity.get_start_time(),
-         activity.get_finish_time());
-      });
+.. code-block:: cpp
+
+   e.load_platform(argv[1]);
+
+  /* Mark all hosts as sequential, as it ought to be in such a scheduling example.
+   *
+   * It means that the hosts can only compute one thing at a given time. If an execution already takes place on a given
+   * host, any subsequently started execution will be queued until after the first execution terminates */
+  for (auto const& host : e.get_all_hosts()) {
+    host->set_concurrency_limit(1);
+    host->set_data(new double(0.0));
+  }
+
+The tasks are imported from a DAX file.
+
+.. code-block:: cpp

 
 

+  /* load the DAX file */
+  auto dax = sg4::create_DAG_from_DAX(argv[2]);
+
+We look for the best host for the root task and schedule it. 
+We then advance the simulation to unlock next schedulable tasks.
+
+.. code-block:: cpp
+
+  /* Schedule the root first */
+  double finish_time;
+  auto* root = static_cast<sg4::Exec*>(dax.front().get());
+  auto host  = get_best_host(root, &finish_time);
+  schedule_on(root, host);
+  e.run();
+
+Then, we get to the major loop of the algorithm.
+This loop goes on until all tasks have been scheduled and executed.
+It starts by finding ready tasks using `get_ready_tasks`. 
+It iteratively looks for the task that will finish first among ready tasks using `get_best_host`, and place it using `schedule_on`. 
+When no more tasks can be placed, we advance the simulation.
+
+.. code-block:: cpp
+
+  while (not vetoed.empty()) {
+    XBT_DEBUG("Start new scheduling round");
+    /* Get the set of ready tasks */
+    auto ready_tasks = get_ready_tasks(dax);
+    vetoed.clear();
+
+    if (ready_tasks.empty()) {
+      /* there is no ready exec, let advance the simulation */

       e.run();
       e.run();

-      return 0;
-   }
+      continue;
+    }
+    /* For each ready exec:
+     * get the host that minimizes the completion time.
+     * select the exec that has the minimum completion time on its best host.
+     */
+    double min_finish_time   = std::numeric_limits<double>::max();
+    sg4::Exec* selected_task = nullptr;
+    sg4::Host* selected_host = nullptr;
+
+    for (auto exec : ready_tasks) {
+      XBT_DEBUG("%s is ready", exec->get_cname());
+      double finish_time;
+      host = get_best_host(exec, &finish_time);
+      if (finish_time < min_finish_time) {
+        min_finish_time = finish_time;
+        selected_task   = exec;
+        selected_host   = host;
+      }
+    }
+
+    XBT_INFO("Schedule %s on %s", selected_task->get_cname(), selected_host->get_cname());
+    schedule_on(selected_task, selected_host, min_finish_time);
+
+    ready_tasks.clear();
+    e.run();
+  }
+
+Finally, we clean up the memory.
+
+.. code-block:: cpp
+
+   /* Cleanup memory */
+   for (auto const& h : e.get_all_hosts())
+     delete h->get_data<double>();
+
+
+
+
+
+