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powerpc: Optimize lock elision for pthread_mutex_t

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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.
This commit is contained in:
Paul Murphy
2015-09-03 13:40:21 -05:00
committed by Tulio Magno Quites Machado Filho
parent e5e6bea22a
commit fadd2ad9cc
5 changed files with 27 additions and 6 deletions
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sysdeps/unix/sysv/linux/powerpc/elision-lock.c
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@ -47,7 +47,6 @@ __lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
{
if (*adapt_count > 0)
{
(*adapt_count)--;
goto use_lock;
}