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authorNick Piggin <npiggin@suse.de>2008-10-21 10:59:15 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2008-10-23 09:18:20 -0700
commita8ddac7e53e89cb877965097d05adfeb1c91def3 (patch)
treedb4ee686e50f7fb57b0cef20e0a8e7f06151e317 /include
parent5a439c565799cb8d290d71ce375e86be64d43a4b (diff)
downloadlinux-linaro-a8ddac7e53e89cb877965097d05adfeb1c91def3.tar.gz
mutex: speed up generic mutex implementations
- atomic operations which both modify the variable and return something imply full smp memory barriers before and after the memory operations involved (failing atomic_cmpxchg, atomic_add_unless, etc don't imply a barrier because they don't modify the target). See Documentation/atomic_ops.txt. So remove extra barriers and branches. - All architectures support atomic_cmpxchg. This has no relation to __HAVE_ARCH_CMPXCHG. We can just take the atomic_cmpxchg path unconditionally This reduces a simple single threaded fastpath lock+unlock test from 590 cycles to 203 cycles on a ppc970 system. Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/asm-generic/mutex-dec.h26
-rw-r--r--include/asm-generic/mutex-xchg.h9
2 files changed, 3 insertions, 32 deletions
diff --git a/include/asm-generic/mutex-dec.h b/include/asm-generic/mutex-dec.h
index ed108be6743..f104af7cf43 100644
--- a/include/asm-generic/mutex-dec.h
+++ b/include/asm-generic/mutex-dec.h
@@ -22,8 +22,6 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
if (unlikely(atomic_dec_return(count) < 0))
fail_fn(count);
- else
- smp_mb();
}
/**
@@ -41,10 +39,7 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
{
if (unlikely(atomic_dec_return(count) < 0))
return fail_fn(count);
- else {
- smp_mb();
- return 0;
- }
+ return 0;
}
/**
@@ -63,7 +58,6 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
static inline void
__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
- smp_mb();
if (unlikely(atomic_inc_return(count) <= 0))
fail_fn(count);
}
@@ -88,25 +82,9 @@ __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
static inline int
__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
{
- /*
- * We have two variants here. The cmpxchg based one is the best one
- * because it never induce a false contention state. It is included
- * here because architectures using the inc/dec algorithms over the
- * xchg ones are much more likely to support cmpxchg natively.
- *
- * If not we fall back to the spinlock based variant - that is
- * just as efficient (and simpler) as a 'destructive' probing of
- * the mutex state would be.
- */
-#ifdef __HAVE_ARCH_CMPXCHG
- if (likely(atomic_cmpxchg(count, 1, 0) == 1)) {
- smp_mb();
+ if (likely(atomic_cmpxchg(count, 1, 0) == 1))
return 1;
- }
return 0;
-#else
- return fail_fn(count);
-#endif
}
#endif
diff --git a/include/asm-generic/mutex-xchg.h b/include/asm-generic/mutex-xchg.h
index 7b9cd2cbfeb..580a6d35c70 100644
--- a/include/asm-generic/mutex-xchg.h
+++ b/include/asm-generic/mutex-xchg.h
@@ -27,8 +27,6 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
if (unlikely(atomic_xchg(count, 0) != 1))
fail_fn(count);
- else
- smp_mb();
}
/**
@@ -46,10 +44,7 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
{
if (unlikely(atomic_xchg(count, 0) != 1))
return fail_fn(count);
- else {
- smp_mb();
- return 0;
- }
+ return 0;
}
/**
@@ -67,7 +62,6 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
static inline void
__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
{
- smp_mb();
if (unlikely(atomic_xchg(count, 1) != 0))
fail_fn(count);
}
@@ -110,7 +104,6 @@ __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
if (prev < 0)
prev = 0;
}
- smp_mb();
return prev;
}