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Don't use a non-locked pre-test of the spinlock on x86_64 machines.

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The pre-test has been shown to be a big loss on Opterons and at best a
wash on EM64T.
This commit is contained in:
Tom Lane 2005-10-11 20:01:30 +00:00
parent 0cc0d0822d
commit 9907b9775b
1 changed files with 50 additions and 4 deletions
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54
src/include/storage/s_lock.h
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@ -66,7 +66,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.140 2005/08/29 00:41:34 tgl Exp $
* $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.141 2005/10/11 20:01:30 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -108,7 +108,7 @@
*/
#if defined(__i386__) || defined(__x86_64__) /* AMD Opteron */
#ifdef __i386__
#define HAS_TEST_AND_SET
typedef unsigned char slock_t;
@ -120,7 +120,11 @@ tas(volatile slock_t *lock)
{
register slock_t _res = 1;
/* Use a non-locking test before asserting the bus lock */
/*
* Use a non-locking test before asserting the bus lock. Note that the
* extra test appears to be a small loss on some x86 platforms and a small
* win on others; it's by no means clear that we should keep it.
*/
__asm__ __volatile__(
" cmpb $0,%1 \n"
" jne 1f \n"
@ -165,7 +169,49 @@ spin_delay(void)
" rep; nop \n");
}
#endif /* __i386__ || __x86_64__ */
#endif /* __i386__ */
#ifdef __x86_64__ /* AMD Opteron, Intel EM64T */
#define HAS_TEST_AND_SET
typedef unsigned char slock_t;
#define TAS(lock) tas(lock)
static __inline__ int
tas(volatile slock_t *lock)
{
register slock_t _res = 1;
/*
* On Opteron, using a non-locking test before the locking instruction
* is a huge loss. On EM64T, it appears to be a wash or small loss,
* so we needn't bother to try to distinguish the sub-architectures.
*/
__asm__ __volatile__(
" lock \n"
" xchgb %0,%1 \n"
: "+q"(_res), "+m"(*lock)
:
: "memory", "cc");
return (int) _res;
}
#define SPIN_DELAY() spin_delay()
static __inline__ void
spin_delay(void)
{
/*
* Adding a PAUSE in the spin delay loop is demonstrably a no-op on
* Opteron, but it may be of some use on EM64T, so we keep it.
*/
__asm__ __volatile__(
" rep; nop \n");
}
#endif /* __x86_64__ */
#if defined(__ia64__) || defined(__ia64)