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[PATCH] Add __glibc_unlikely hint in lll_trylock, lll_cond_trylock.
- From: Stefan Liebler <stli at linux dot vnet dot ibm dot com>
- To: libc-alpha at sourceware dot org
- Date: Tue, 13 Dec 2016 09:54:42 +0100
- Subject: [PATCH] Add __glibc_unlikely hint in lll_trylock, lll_cond_trylock.
- Authentication-results: sourceware.org; auth=none
Hi,
the macros lll_trylock, lll_cond_trylock are extended by a
__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.
Okay to commit?
Bye
Stefan
ChangeLog:
* sysdeps/nptl/lowlevellock.h (lll_trylock, lll_cond_trylock):
Add __glibc_unlikely hint.
commit 2e11862aaf6d563518780a470b97b59a6e0b2717
Author: Stefan Liebler <stli@linux.vnet.ibm.com>
Date: Tue Dec 13 09:14:09 2016 +0100
Add __glibc_unlikely hint in lll_trylock, lll_cond_trylock.
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.
diff --git a/sysdeps/nptl/lowlevellock.h b/sysdeps/nptl/lowlevellock.h
index 3890145..b77043b 100644
--- a/sysdeps/nptl/lowlevellock.h
+++ b/sysdeps/nptl/lowlevellock.h
@@ -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;