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author | Rogerio Alves <rcardoso@linux.vnet.ibm.com> | 2017-12-05 14:24:14 -0200 |
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committer | Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com> | 2017-12-05 17:48:48 -0200 |
commit | 07ed18d26a342741cb25a4739158c65ed9dd4d09 (patch) | |
tree | fb40f10305dcd58b492bf0b685b29b37266bc8c8 /manual/tunables.texi | |
parent | a5a2a76bb71940cb8ceb4769a975327027fd55b5 (diff) | |
download | glibc-07ed18d26a342741cb25a4739158c65ed9dd4d09.tar.gz glibc-07ed18d26a342741cb25a4739158c65ed9dd4d09.tar.xz glibc-07ed18d26a342741cb25a4739158c65ed9dd4d09.zip |
Add elision tunables
This patch adds several new tunables to control the behavior of elision on supported platforms[1]. Since elision now depends on tunables, we should always *compile* with elision enabled, and leave the code disabled, but available for runtime selection. This gives us *much* better compile-time testing of the existing code to avoid bit-rot[2]. Tested on ppc, ppc64, ppc64le, s390x and x86_64. [1] This part of the patch was initially proposed by Paul Murphy but was "staled" because the framework have changed since the patch was originally proposed: https://patchwork.sourceware.org/patch/10342/ [2] This part of the patch was inititally proposed as a RFC by Carlos O'Donnell. Make sense to me integrate this on the patch: https://sourceware.org/ml/libc-alpha/2017-05/msg00335.html * elf/dl-tunables.list: Add elision parameters. * manual/tunables.texi: Add entries about elision tunable. * sysdeps/unix/sysv/linux/powerpc/elision-conf.c: Add callback functions to dynamically enable/disable elision. Add multiple callbacks functions to set elision parameters. Deleted __libc_enable_secure check. * sysdeps/unix/sysv/linux/s390/elision-conf.c: Likewise. * sysdeps/unix/sysv/linux/x86/elision-conf.c: Likewise. * configure: Regenerated. * configure.ac: Option enable_lock_elision was deleted. * config.h.in: ENABLE_LOCK_ELISION flag was deleted. * config.make.in: Remove references to enable_lock_elision. * manual/install.texi: Elision configure option was removed. * INSTALL: Regenerated to remove enable_lock_elision. * nptl/Makefile: Disable elision so it can verify error case for destroying a mutex. * sysdeps/powerpc/nptl/elide.h: Cleanup ENABLE_LOCK_ELISION check. Deleted macros for the case when ENABLE_LOCK_ELISION was not defined. * sysdeps/s390/configure: Regenerated. * sysdeps/s390/configure.ac: Remove references to enable_lock_elision.. * nptl/tst-mutex8.c: Deleted all #ifndef ENABLE_LOCK_ELISION from the test. * sysdeps/powerpc/powerpc32/sysdep.h: Deleted all ENABLE_LOCK_ELISION checks. * sysdeps/powerpc/powerpc64/sysdep.h: Likewise. * sysdeps/powerpc/sysdep.h: Likewise. * sysdeps/s390/nptl/bits/pthreadtypes-arch.h: Likewise. * sysdeps/unix/sysv/linux/powerpc/force-elision.h: Likewise. * sysdeps/unix/sysv/linux/s390/elision-conf.h: Likewise. * sysdeps/unix/sysv/linux/s390/force-elision.h: Likewise. * sysdeps/unix/sysv/linux/s390/lowlevellock.h: Likewise. * sysdeps/unix/sysv/linux/s390/Makefile: Remove references to enable-lock-elision. Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
Diffstat (limited to 'manual/tunables.texi')
-rw-r--r-- | manual/tunables.texi | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/manual/tunables.texi b/manual/tunables.texi index f503daef56..e851b95c59 100644 --- a/manual/tunables.texi +++ b/manual/tunables.texi @@ -31,6 +31,7 @@ their own namespace. @menu * Tunable names:: The structure of a tunable name * Memory Allocation Tunables:: Tunables in the memory allocation subsystem +* Elision Tunables:: Tunables in elision subsystem * Hardware Capability Tunables:: Tunables that modify the hardware capabilities seen by @theglibc{} @end menu @@ -212,6 +213,74 @@ pre-fill the per-thread cache with. The default, or when set to zero, is no limit. @end deftp +@node Elision Tunables +@section Elision Tunables +@cindex elision tunables +@cindex tunables, elision + +@deftp {Tunable namespace} glibc.elision +Contended locks are usually slow and can lead to performance and scalability +issues in multithread code. Lock elision will use memory transactions to under +certain conditions, to elide locks and improve performance. +Elision behavior can be modified by setting the following tunables in +the @code{elision} namespace: +@end deftp + +@deftp Tunable glibc.elision.enable +The @code{glibc.elision.enable} tunable enables lock elision if the feature is +supported by the hardware. If elision is not supported by the hardware this +tunable has no effect. + +Elision tunables are supported for 64-bit Intel, IBM POWER, and z System +architectures. +@end deftp + +@deftp Tunable glibc.elision.skip_lock_busy +The @code{glibc.elision.skip_lock_busy} tunable sets how many times to use a +non-transactional lock after a transactional failure has occurred because the +lock is already acquired. Expressed in number of lock acquisition attempts. + +The default value of this tunable is @samp{3}. +@end deftp + +@deftp Tunable glibc.elision.skip_lock_internal_abort +The @code{glibc.elision.skip_lock_internal_abort} tunable sets how many times +the thread should avoid using elision if a transaction aborted for any reason +other than a different thread's memory accesses. Expressed in number of lock +acquisition attempts. + +The default value of this tunable is @samp{3}. +@end deftp + +@deftp Tunable glibc.elision.skip_lock_after_retries +The @code{glibc.elision.skip_lock_after_retries} tunable sets how many times +to try to elide a lock with transactions, that only failed due to a different +thread's memory accesses, before falling back to regular lock. +Expressed in number of lock elision attempts. + +This tunable is supported only on IBM POWER, and z System architectures. + +The default value of this tunable is @samp{3}. +@end deftp + +@deftp Tunable glibc.elision.tries +The @code{glibc.elision.tries} sets how many times to retry elision if there is +chance for the transaction to finish execution e.g., it wasn't +aborted due to the lock being already acquired. If elision is not supported +by the hardware this tunable is set to @samp{0} to avoid retries. + +The default value of this tunable is @samp{3}. +@end deftp + +@deftp Tunable glibc.elision.skip_trylock_internal_abort +The @code{glibc.elision.skip_trylock_internal_abort} tunable sets how many +times the thread should avoid trying the lock if a transaction aborted due to +reasons other than a different thread's memory accesses. Expressed in number +of try lock attempts. + +The default value of this tunable is @samp{3}. +@end deftp + @node Hardware Capability Tunables @section Hardware Capability Tunables @cindex hardware capability tunables |