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Underline importance of NUM_THREADS setting for BUFFER allocation 

following augray's suggestion from #1451, and incorporating ashwinyes' comments from #1141 on the importance of NUM_THREADS even for single-threaded builds.
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Martin Kroeker 2018-04-04 22:26:51 +02:00 committed by GitHub
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USAGE.md
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@ -14,6 +14,20 @@ Please build OpenBLAS with larger `NUM_THREADS`. For example, `make
NUM_THREADS=32` or `make NUM_THREADS=64`. In `Makefile.system`, we will set NUM_THREADS=32` or `make NUM_THREADS=64`. In `Makefile.system`, we will set
`MAX_CPU_NUMBER=NUM_THREADS`. `MAX_CPU_NUMBER=NUM_THREADS`.
Despite its name, and due to the use of memory buffers in functions like SGEMM,
the setting of NUM_THREADS can be relevant even for a single-threaded build
of OpenBLAS, if such functions get called by multiple threads of a program
that uses OpenBLAS. In some cases, the affected code may simply crash or throw
a segmentation fault without displaying the above warning first.
Note that the number of threads used at runtime can be altered to differ from the
value NUM_THREADS was set to at build time. At runtime, the actual number of
threads can be set anywhere from 1 to the build's NUM_THREADS (note however,
that this does not change the number of memory buffers that will be allocated,
which is set at build time). The number of threads for a process can be set by
using the mechanisms described below.
#### How can I use OpenBLAS in multi-threaded applications? #### How can I use OpenBLAS in multi-threaded applications?
If your application is already multi-threaded, it will conflict with OpenBLAS If your application is already multi-threaded, it will conflict with OpenBLAS