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Add __glibc_unlikely hint in lll_trylock, lll_cond_trylock.

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The macros lll_trylock, lll_cond_trylock are extended by an __glibc_unlikely
hint.  Now the trylock macros are based on the same assumption about a
free/busy lock as lll_lock.
With the hint gcc emits code in e.g. pthread_mutex_trylock which does
not use jumps if the lock is free.  Without the hint it had to jump away
if the lock is free.

Tested on s390x, ppc.

ChangeLog:

	* sysdeps/nptl/lowlevellock.h (lll_trylock, lll_cond_trylock):
	Add __glibc_unlikely hint.
This commit is contained in:
Stefan Liebler 2017-02-06 13:44:23 +01:00
parent f2d7f23a30
commit df3a4e104f
2 changed files with 7 additions and 2 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
2017-02-06 Stefan Liebler <stli@linux.vnet.ibm.com>
* sysdeps/nptl/lowlevellock.h (lll_trylock, lll_cond_trylock):
Add __glibc_unlikely hint.
2017-02-06 Adhemerval Zanella <adhemerval.zanella@linaro.org>
[BZ #16640]

4
sysdeps/nptl/lowlevellock.h
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@ -64,13 +64,13 @@
0. Otherwise leave lock unchanged and return non-zero to indicate that the
lock was not acquired. */
#define lll_trylock(lock) \
atomic_compare_and_exchange_bool_acq (&(lock), 1, 0)
__glibc_unlikely (atomic_compare_and_exchange_bool_acq (&(lock), 1, 0))
/* If LOCK is 0 (not acquired), set to 2 (acquired, possibly with waiters) and
return 0. Otherwise leave lock unchanged and return non-zero to indicate
that the lock was not acquired. */
#define lll_cond_trylock(lock) \
atomic_compare_and_exchange_bool_acq (&(lock), 2, 0)
__glibc_unlikely (atomic_compare_and_exchange_bool_acq (&(lock), 2, 0))
extern void __lll_lock_wait_private (int *futex) attribute_hidden;
extern void __lll_lock_wait (int *futex, int private) attribute_hidden;