X-Git-Url: https://bilbo.iut-bm.univ-fcomte.fr/and/gitweb/prng_gpu.git/blobdiff_plain/4f77fbaca003dceaba9d6c5f8c6695327b1e2113..a97a587bc408ff330d3c6292bcf7d0c488ecae16:/prng_gpu.tex diff --git a/prng_gpu.tex b/prng_gpu.tex index 82a4927..d95e87f 100644 --- a/prng_gpu.tex +++ b/prng_gpu.tex @@ -817,8 +817,8 @@ the larger the number of threads is, the more local memory is used and the less branching instructions are used (if, while, ...), the better performance is obtained on GPU. So with algorithm \ref{algo:seqCIprng} presented in the previous section, it is possible to build a similar program which computes PRNG -on GPU. In the CUDA [ref] environment, threads have a local identificator, -called \texttt{ThreadIdx} relative to the block containing them. +on GPU. In the CUDA~\cite{Nvid10} environment, threads have a local +identificator, called \texttt{ThreadIdx} relative to the block containing them. \subsection{Naive version for GPU} @@ -828,14 +828,14 @@ The principe consists in assigning the computation of a PRNG as in sequential to each thread of the GPU. Of course, it is essential that the three xor-like PRNGs used for our computation have different parameters. So we chose them randomly with another PRNG. As the initialisation is performed by the CPU, we -have chosen to use the ISAAC PRNG [ref] to initalize all the parameters for the -GPU version of our PRNG. The implementation of the three xor-like PRNGs is -straightforward as soon as their parameters have been allocated in the GPU -memory. Each xor-like PRNGs used works with an internal number $x$ which keeps -the last generated random numbers. Other internal variables are also used by the -xor-like PRNGs. More precisely, the implementation of the xor128, the xorshift -and the xorwow respectively require 4, 5 and 6 unsigned long as internal -variables. +have chosen to use the ISAAC PRNG~\ref{Jenkins96} to initalize all the +parameters for the GPU version of our PRNG. The implementation of the three +xor-like PRNGs is straightforward as soon as their parameters have been +allocated in the GPU memory. Each xor-like PRNGs used works with an internal +number $x$ which keeps the last generated random numbers. Other internal +variables are also used by the xor-like PRNGs. More precisely, the +implementation of the xor128, the xorshift and the xorwow respectively require +4, 5 and 6 unsigned long as internal variables. \begin{algorithm} @@ -895,7 +895,7 @@ which represent the indexes of the other threads for which the results are used by the current thread. In the algorithm, we consider that a 64-bits xor-like PRNG is used, that is why both 32-bits parts are used. -This version also succeed to the BigCrush batteries of tests. +This version also succeeds to the {\it BigCrush} batteries of tests. \begin{algorithm} @@ -906,17 +906,15 @@ tab1, tab2: Arrays containing permutations of size permutation\_size\;} \KwOut{NewNb: array containing random numbers in global memory} \If{threadId is concerned} { - retrieve data from InternalVarXorLikeArray[threadId] in local variables\; + retrieve data from InternalVarXorLikeArray[threadId] in local variables including shared memory\; offset = threadIdx\%permutation\_size\; o1 = threadIdx-offset+tab1[offset]\; o2 = threadIdx-offset+tab2[offset]\; \For{i=1 to n} { t=xor-like()\; - shared\_mem[threadId]=(unsigned int)t\; - x = x $\oplus$ (unsigned int) t\; - x = x $\oplus$ (unsigned int) (t>>32)\; - x = x $\oplus$ shared[o1]\; - x = x $\oplus$ shared[o2]\; + t=t$\oplus$shmem[o1]$\oplus$shmem[o2]\; + shared\_mem[threadId]=t\; + x = x $\oplus$ t\; store the new PRNG in NewNb[NumThreads*threadId+i]\; } @@ -930,9 +928,9 @@ version} \subsection{Theoretical Evaluation of the Improved Version} -A run of Algorithm~\ref{algo:gpu_kernel2} consists in four operations having +A run of Algorithm~\ref{algo:gpu_kernel2} consists in three operations having the form of Equation~\ref{equation Oplus}, which is equivalent to the iterative -system of Eq.~\ref{eq:generalIC}. That is, four iterations of the general chaotic +system of Eq.~\ref{eq:generalIC}. That is, three iterations of the general chaotic iterations are realized between two stored values of the PRNG. To be certain that we are in the framework of Theorem~\ref{t:chaos des general}, we must guarantee that this dynamical system iterates on the space @@ -954,8 +952,25 @@ Devaney's formulation of a chaotic behavior. \section{Experiments} \label{sec:experiments} -Different experiments have been performed in order to measure the generation -speed. In Figure~\ref{fig:time_gpu} we compare the number of random numbers generated per second. +Different experiments have been performed in order to measure the generation +speed. We have used a computer equiped with Tesla C1060 NVidia GPU card and an +Intel Xeon E5530 cadenced at 2.40 GHz for our experiments and we have used +another one equipped with a less performant CPU and a GeForce GTX 280. Both +cards have 240 cores. + +In Figure~\ref{fig:time_gpu} we compare the number of random numbers generated +per second. The xor-like prng is a xor64 described in~\cite{Marsaglia2003}. In +order to obtain the optimal performance we remove the storage of random numbers +in the GPU memory. This step is time consumming and slows down the random number +generation. Moreover, if you are interested by applications that consome random +numbers directly when they are generated, their storage is completely +useless. In this figure we can see that when the number of threads is greater +than approximately 30,000 upto 5 millions the number of random numbers generated +per second is almost constant. With the naive version, it is between 2.5 and +3GSample/s. With the optimized version, it is approximately equals to +20GSample/s. Finally we can remark that both GPU cards are quite similar. In +practice, the Tesla C1060 has more memory than the GTX 280 and this memory +should be of better quality. \begin{figure}[htbp] \begin{center} @@ -966,11 +981,10 @@ speed. In Figure~\ref{fig:time_gpu} we compare the number of random numbers gene \end{figure} -First of all we have compared the time to generate X random numbers with both -the CPU version and the GPU version. +In comparison, Listing~\ref{algo:seqCIprng} allows us to generate about +138MSample/s with only one core of the Xeon E5530. + -Faire une courbe du nombre de random en fonction du nombre de threads, -éventuellement en fonction du nombres de threads par bloc.