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lockref: use arch_mutex_cpu_relax() in CMPXCHG_LOOP()

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Make use of arch_mutex_cpu_relax() so architectures can override the
default cpu_relax() semantics.
This is especially useful for s390, where cpu_relax() means that we
yield() the current (virtual) cpu and therefore is very expensive,
and would contradict the whole purpose of the lockless cmpxchg loop.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
This commit is contained in:
Heiko Carstens 2013-09-23 12:59:56 +02:00
parent 083986e824
commit 491f6f8e5f
1 changed files with 9 additions and 1 deletions
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10
lib/lockref.c
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@ -11,6 +11,14 @@
# define cmpxchg64_relaxed cmpxchg64 # define cmpxchg64_relaxed cmpxchg64
#endif #endif
/*
* Allow architectures to override the default cpu_relax() within CMPXCHG_LOOP.
* This is useful for architectures with an expensive cpu_relax().
*/
#ifndef arch_mutex_cpu_relax
# define arch_mutex_cpu_relax() cpu_relax()
#endif
/* /*
* Note that the "cmpxchg()" reloads the "old" value for the * Note that the "cmpxchg()" reloads the "old" value for the
* failure case. * failure case.
@ -28,7 +36,7 @@
if (likely(old.lock_count == prev.lock_count)) { \ if (likely(old.lock_count == prev.lock_count)) { \
SUCCESS; \ SUCCESS; \
} \ } \
cpu_relax(); \ arch_mutex_cpu_relax(); \
} \ } \
} while (0) } while (0)