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package/openblas: allow disabling multithreading

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Buildroot would automatically enable multithreading in OpenBLAS if the
architecture supports it. However, one may want to avoid OpenBLAS creating
threads itself and configure single-threaded operation. To accommodate this
use case, add a config option for multithreading.

When multithreading is disabled but OpenBLAS functions are called in the
same application by multiple threads, then locking is mandatory. The
USE_LOCKING flag was added in version 0.3.7 with following release note:

    a new option USE_LOCKING was added to ensure thread safety when OpenBLAS
    itself is built without multithreading but will be called from multiple
    threads.

However, if one knows that OpenBLAS will only be called from single-threaded
applications, then passing USE_LOCKING is not necessary, so make it a config
option too.

When multithreading is enabled, locking is implicitly enabled inside
openblas, so only provide the locking option when multithreading is
disabled.

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
This commit is contained in:
Thomas De Schampheleire 2021-02-12 10:15:09 +01:00 committed by Thomas Petazzoni
parent 7d73bc5216
commit 6f29cdeee4
2 changed files with 29 additions and 1 deletions
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21
package/openblas/Config.in
View File

@ -73,4 +73,25 @@ config BR2_PACKAGE_OPENBLAS_TARGET
string "OpenBLAS target CPU"
default BR2_PACKAGE_OPENBLAS_DEFAULT_TARGET
config BR2_PACKAGE_OPENBLAS_USE_THREAD
bool "use multithreading"
default y
depends on BR2_TOOLCHAIN_HAS_THREADS
depends on !BR2_STATIC_LIBS
help
Tell OpenBLAS to use multithreading, by passing USE_THREAD=1.
config BR2_PACKAGE_OPENBLAS_USE_LOCKING
bool "use locking"
default y
depends on BR2_TOOLCHAIN_HAS_THREADS
depends on !BR2_PACKAGE_OPENBLAS_USE_THREAD
help
Tell OpenBLAS to use locking, by passing USE_LOCKING=1.
Locking is implicitly enabled when USE_THREAD=1.
However, if USE_THREAD=0 (i.e. OpenBLAS itself will run in
single-threaded mode) but an application makes OpenBLAS
function calls from multiple threads, then locking is
mandatory for correct operation.
endif

9
package/openblas/openblas.mk
View File

@ -25,12 +25,19 @@ OPENBLAS_MAKE_OPTS += ONLY_CBLAS=1
endif
# Enable/Disable multi-threading (not for static-only since it uses dlfcn.h)
ifeq ($(BR2_TOOLCHAIN_HAS_THREADS):$(BR2_STATIC_LIBS),y:)
ifeq ($(BR2_PACKAGE_OPENBLAS_USE_THREAD),y)
OPENBLAS_MAKE_OPTS += USE_THREAD=1
else
OPENBLAS_MAKE_OPTS += USE_THREAD=0
endif
ifeq ($(BR2_PACKAGE_OPENBLAS_USE_LOCKING),y)
OPENBLAS_MAKE_OPTS += USE_LOCKING=1
else
# not passing USE_LOCKING=0 as this could be confusing: its effect is implicit
# in case of USE_THREAD=1.
endif
# We don't know if OpenMP is available or not, so disable
OPENBLAS_MAKE_OPTS += USE_OPENMP=0