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x86: Use asm goto to implement better modify_and_test() functions

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Linus suggested using asm goto to get rid of the typical SETcc + TEST
instruction pair -- which also clobbers an extra register -- for our
typical modify_and_test() functions.

Because asm goto doesn't allow output fields it has to include an
unconditinal memory clobber when it changes a memory variable to force
a reload.

Luckily all atomic ops already imply a compiler barrier to go along
with their memory barrier semantics.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-0mtn9siwbeo1d33bap1422se@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra
2013-09-11 15:19:24 +02:00
committed by Ingo Molnar
parent 4314895165
commit 0c44c2d0f4
5 changed files with 58 additions and 92 deletions
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29
arch/x86/include/asm/atomic.h
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@@ -6,6 +6,7 @@
#include <asm/processor.h>
#include <asm/alternative.h>
#include <asm/cmpxchg.h>
#include <asm/rmwcc.h>
/*
* Atomic operations that C can't guarantee us. Useful for
@@ -76,12 +77,7 @@ static inline void atomic_sub(int i, atomic_t *v)
*/
static inline int atomic_sub_and_test(int i, atomic_t *v)
{
unsigned char c;
asm volatile(LOCK_PREFIX "subl %2,%0; sete %1"
: "+m" (v->counter), "=qm" (c)
: "ir" (i) : "memory");
return c;
GEN_BINARY_RMWcc(LOCK_PREFIX "subl", v->counter, i, "%0", "e");
}
/**
@@ -118,12 +114,7 @@ static inline void atomic_dec(atomic_t *v)
*/
static inline int atomic_dec_and_test(atomic_t *v)
{
unsigned char c;
asm volatile(LOCK_PREFIX "decl %0; sete %1"
: "+m" (v->counter), "=qm" (c)
: : "memory");
return c != 0;
GEN_UNARY_RMWcc(LOCK_PREFIX "decl", v->counter, "%0", "e");
}
/**
@@ -136,12 +127,7 @@ static inline int atomic_dec_and_test(atomic_t *v)
*/
static inline int atomic_inc_and_test(atomic_t *v)
{
unsigned char c;
asm volatile(LOCK_PREFIX "incl %0; sete %1"
: "+m" (v->counter), "=qm" (c)
: : "memory");
return c != 0;
GEN_UNARY_RMWcc(LOCK_PREFIX "incl", v->counter, "%0", "e");
}
/**
@@ -155,12 +141,7 @@ static inline int atomic_inc_and_test(atomic_t *v)
*/
static inline int atomic_add_negative(int i, atomic_t *v)
{
unsigned char c;
asm volatile(LOCK_PREFIX "addl %2,%0; sets %1"
: "+m" (v->counter), "=qm" (c)
: "ir" (i) : "memory");
return c;
GEN_BINARY_RMWcc(LOCK_PREFIX "addl", v->counter, i, "%0", "s");
}
/**