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Update OpenBLAS build options #5091

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merged 1 commit into from Jul 17, 2019
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Update OpenBLAS build options #5091

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6 changes: 3 additions & 3 deletions OpenBLAS.spec
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Expand Up @@ -10,12 +10,12 @@ Source: https://github.com/xianyi/OpenBLAS/archive/v%{realversion}.tar.gz

# PRESCOTT is a generic x86-64 target https://github.com/xianyi/OpenBLAS/issues/685
%ifarch x86_64
make FC=gfortran BINARY=64 TARGET=PENRYN NUM_THREADS=256 DYNAMIC_ARCH=1
make FC=gfortran BINARY=64 TARGET=CORE2 NUM_THREADS=256 DYNAMIC_ARCH=0
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what does the NUM_THREADS actually correspond to in reality at run time?
Was the speedup seen in tests of deepAK8 real or a simple parallelization on a quiet node?

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@slava77 What affects the number of threads used at runtime is the OPENBLAS_NUM_THREADS environment variable which is set to 1 in https://github.com/cms-sw/cmsdist/blob/IB/CMSSW_11_0_X/gcc700/OpenBLAS-toolfile.spec#L19. NUM_THREADS is the maximum allowed number of threads and is used for resource allocation etc. I explicitly checked the CPU usage when running the tests and it was not going beyond 100%:)

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And gslblas is known to be not a very high-performance BLAS routine, so the speed-up we saw after switching to OpenBLAS should not be surprising at all.

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thanks for clarifications

%else
%ifarch aarch64
make FC=gfortran BINARY=64 TARGET=ARMV8 NUM_THREADS=256 DYNAMIC_ARCH=1
make FC=gfortran BINARY=64 TARGET=ARMV8 NUM_THREADS=256 DYNAMIC_ARCH=0
%else
make FC=gfortran BINARY=64 NUM_THREADS=256 DYNAMIC_ARCH=1
make FC=gfortran BINARY=64 NUM_THREADS=256 DYNAMIC_ARCH=0
%endif # aarch64
%endif # x86_64

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