Hi,
since 13.4 and 13.5 beta, my OpenCL GPU program consumes ~80% of one CPU core while in clFinish, waiting for a string of GPU kernels and a final clEnqueueReadBuffer. My main thread looks like this
ntdll.dll!NtWaitForSingleObject+0xa
KERNELBASE.dll!WaitForSingleObjectEx+0x9c
amdocl64.dll!clGetSamplerInfo+0x1031c
amdocl64.dll!clGetSamplerInfo+0x101f8
amdocl64.dll!clGetSamplerInfo+0x120ea
amdocl64.dll!clGetSamplerInfo+0x4b51
amdocl64.dll!clFinish+0x89
mfakto.exe!tf_class_opencl+0xf94
mfakto.exe!tf+0x583
mfakto.exe!main+0x117d
mfakto.exe!__tmainCRTStartup+0x11a
kernel32.dll!BaseThreadInitThunk+0xd
ntdll.dll!RtlUserThreadStart+0x21
and is using 0.01% CPU.
However, there is another thread:
amdocl64.dll!clIcdGetPlatformIDsKHR+0x3e5
amdocl64.dll!clGetSamplerInfo+0x49cf
amdocl64.dll!clGetSamplerInfo+0x38af2
amdocl64.dll!clGetSamplerInfo+0x38d18
amdocl64.dll!clGetSamplerInfo+0x504e
amdocl64.dll!clGetSamplerInfo+0x5172
amdocl64.dll!clGetSamplerInfo+0x1ccf
kernel32.dll!BaseThreadInitThunk+0xd
ntdll.dll!RtlUserThreadStart+0x21
that is using ~19% CPU (76% of a core). The upper part of the stack changes - it is not stuck in clIcdGetPlatformIDsKHR.
When using a CPU-hungry program to consume almost all CPU and starve my program, then this thread's CPU load goes back to almost nothing, but the GPU is not fed very well and GPU load is very jumpy between 70-98%. GPU load would normally be pegged at 100%.
When rolling back to cat13.3, the program's total CPU load is at ~0.1-0.3%, and running a CPU-hog has almost no effect on my program.
Is there anything special to be done on the newer drivers to make them leave the CPU alone? Is there any setting to get the CPU-behavior of the previous drivers?
My environment: HD5770+Phenom II X4 955, Win7-64. I got reports that the same happens with an APU and the integrated 6550D (also Win7-64).
Note: Making the final clEnqueueReadBuffer synchronous instead of the final clFinish does not change the CPU load.
... and could someone please give me a hint how I can get a proper code formatting in this forum? Thanks a lot!