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authorRich Felker <dalias@aerifal.cx>2015-08-16 18:15:18 +0000
committerRich Felker <dalias@aerifal.cx>2015-08-16 18:15:18 +0000
commit5a9c8c05a5a0cdced4122589184fd795b761bb4a (patch)
tree34b9f909c151de0d24ec29ef194815a5fa4daede
parentc13f2af1fe1856e36dd1b2773cac05d5d72641dc (diff)
downloadmusl-5a9c8c05a5a0cdced4122589184fd795b761bb4a.tar.gz
mitigate performance regression in libc-internal locks on x86_64
commit 3c43c0761e1725fd5f89a9c028cbf43250abb913 fixed missing synchronization in the atomic store operation for i386 and x86_64, but opted to use mfence for the barrier on x86_64 where it's always available. however, in practice mfence is significantly slower than the barrier approach used on i386 (a nop-like lock orl operation). this commit changes x86_64 (and x32) to use the faster barrier.
-rw-r--r--arch/x32/atomic.h2
-rw-r--r--arch/x86_64/atomic.h2
2 files changed, 2 insertions, 2 deletions
diff --git a/arch/x32/atomic.h b/arch/x32/atomic.h
index 2ab1f7a2..7690183d 100644
--- a/arch/x32/atomic.h
+++ b/arch/x32/atomic.h
@@ -83,7 +83,7 @@ static inline void a_dec(volatile int *x)
static inline void a_store(volatile int *p, int x)
{
- __asm__( "mov %1, %0 ; mfence" : "=m"(*p) : "r"(x) : "memory" );
+ __asm__( "mov %1, %0 ; lock ; orl $0,(%%rsp)" : "=m"(*p) : "r"(x) : "memory" );
}
static inline void a_spin()
diff --git a/arch/x86_64/atomic.h b/arch/x86_64/atomic.h
index 2ab1f7a2..7690183d 100644
--- a/arch/x86_64/atomic.h
+++ b/arch/x86_64/atomic.h
@@ -83,7 +83,7 @@ static inline void a_dec(volatile int *x)
static inline void a_store(volatile int *p, int x)
{
- __asm__( "mov %1, %0 ; mfence" : "=m"(*p) : "r"(x) : "memory" );
+ __asm__( "mov %1, %0 ; lock ; orl $0,(%%rsp)" : "=m"(*p) : "r"(x) : "memory" );
}
static inline void a_spin()