With TLE enabled, the adapt count variable update incurs
an 8% overhead before entering the critical section of an
elided mutex.
Instead, if it is done right after leaving the critical
section, this serialization can be avoided.
This alters the existing behavior of __lll_trylock_elision
as it will only decrement the adapt_count if it successfully
acquires the lock.
* sysdeps/unix/sysv/linux/powerpc/elision-lock.c
(__lll_lock_elision): Remove adapt_count decrement...
* sysdeps/unix/sysv/linux/powerpc/elision-trylock.c
(__lll_trylock_elision): Likewise.
* sysdeps/unix/sysv/linux/powerpc/elision-unlock.c
(__lll_unlock_elision): ... to here. And utilize
new adapt_count parameter.
* sysdeps/unix/sysv/linux/powerpc/lowlevellock.h
(__lll_unlock_elision): Update to include adapt_count
parameter.
(lll_unlock_elision): Pass pointer to adapt_count
variable.
Adding this parameter will give architectures more freedom in
how they choose to update this variable. This change has no
effect on architectures which choose not to use it.
* nptl/pthread_mutex_unlock.c(lll_unlock_elision):
Add elision adapt_count parameter to list of arguments.
* sysdeps/unix/sysv/linux/powerpc/lowlevellock.h
(lll_unlock_elision): Update with new parameter list
* sysdeps/unix/sysv/linux/s390/lowlevellock.h
(lll_unlock_elision): Likewise
* sysdeps/unix/sysv/linux/x86_64/lowlevellock.h
(lll_unlock_elision): Likewise
This patch adds support for lock elision using ISA 2.07 hardware
transactional memory instructions for pthread_mutex primitives.
Similar to s390 version, the for elision logic defined in
'force-elision.h' is only enabled if ENABLE_LOCK_ELISION is defined.
Also, the lock elision code should be able to be built even with
a compiler that does not provide HTM support with builtins.
However I have noted the performance is sub-optimal due scheduling
pressures.
Commit 887865f remove the lll_robust_trylock definition on all
architectures, however for powerpc both __lll_trylock and
__lll_cond_trylock were based on lll_robust_trylock definition.
This patch restore it with a different name.
