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POCan't change array size over 10000 in array additions and performance issue CPU vs GPU
 

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  1. POCan't change array size over 10000 in array additions and performance issue CPU vs GPU
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    <p>I'm new with OpenCL and have some problems with the array additions I use the code provided in the link below</p> <p><a href="http://code.google.com/p/opencl-book-samples/source/browse/#svn%2Ftrunk%2Fsrc%2FChapter_2%2FHelloWorld%253Fstate%253Dclosed" rel="nofollow">http://code.google.com/p/opencl-book-samples/source/browse/#svn%2Ftrunk%2Fsrc%2FChapter_2%2FHelloWorld%253Fstate%253Dclosed</a></p> <p>and I added some parts to measure the performance of the GPU</p> <pre><code>clFinish(commandQueue); // Queue the kernel up for execution across the array cl_ulong start, end; cl_event k_events; errNum = clEnqueueNDRangeKernel(commandQueue, kernel, 1, NULL, globalWorkSize, localWorkSize, 0, NULL, &amp;k_events); clGetEventProfilingInfo(k_events, CL_PROFILING_COMMAND_START, sizeof(cl_ulong), &amp;start, NULL); clWaitForEvents(1 , &amp;k_events); clGetEventProfilingInfo(k_events, CL_PROFILING_COMMAND_END, sizeof(cl_ulong), &amp;end, NULL); clGetEventProfilingInfo(k_events, CL_PROFILING_COMMAND_START, sizeof(cl_ulong), &amp;start, NULL); float GPUTime = (end - start); </code></pre> <p>And this to measure the CPU time</p> <pre><code>LARGE_INTEGER CPUstart, finish, freq; QueryPerformanceFrequency(&amp;freq); QueryPerformanceCounter(&amp;CPUstart); for (int i=0;i&lt;ARRAY_SIZE;i++){ result[i]=a[i]+b[i]; } QueryPerformanceCounter(&amp;finish); double timeCPU=(finish.QuadPart - CPUstart.QuadPart) /((double)freq.QuadPart)/1000000000.0) ; </code></pre> <p>The first problem I encountered is <strong>the array size ; it can't go beyond 10000 ; if I do this ; it just crash</strong> . How to fix it ?</p> <p>The second problem is the performance ; <strong>the GPU/CPU ratio range is too wide ; from 13% to 210%(ish)</strong> . Why does this happen and can you suggest a fix ?</p> <p>Edit : I figured out the 2nd ; the lag was caused by the power saving mode ; it set the core/mem to much lower than default . Just use a program to lock it ; and the performance are rocking stable at ~150-300 % (GPU/CPU)</p> <p>Good case </p> <pre><code>GPU time :632667 nanosecs. CPU time : 990023 nanosecs. GPU/CPU ratio : 156.484 percent. </code></pre> <p>And bad one :</p> <pre><code>GPU time :6.83267e+006 nanosecs. CPU time : 1.00756e+006 nanosecs. GPU/CPU ratio : 14.7462 percent. </code></pre> <p>Any ideas will be appreciated . Thank you :D</p> <p>PS : The CPU is core i3-370M ; GPU : HD5470 . I use VS2008 on windows 7</p>
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    1. USTiana987642
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    1. COWhow. You like outdated dev environments combined with decent OS? THe 5470 may be memory strapped - did you look at the numbers to check you do not overlaod the poor 5470?
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      1. USTomTom
    2. COSo you suggest me update to the newer version of VS ? So I will try
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      1. USTiana987642
    3. COItmaeks little sense to not do it. If it makes sense, go all the way to 20212 - it will be out of release candidate in 2-3 months, so depending on project length it is worth it. It is also fully supported by Microsoft (the GC).
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