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Improve spinlock code for recent x86 processors: insert a PAUSE 

instruction in the s_lock() wait loop, and use test before test-and-set
in TAS() macro to avoid unnecessary bus traffic.  Patch from Manfred
Spraul, reworked a bit by Tom.
This commit is contained in:
Tom Lane 2003-12-27 20:58:58 +00:00
parent 2cdace962b
commit f8eed65dfb
2 changed files with 27 additions and 2 deletions
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6
src/backend/storage/lmgr/s_lock.c
View File

@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/lmgr/s_lock.c,v 1.22 2003/12/23 22:15:07 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/lmgr/s_lock.c,v 1.23 2003/12/27 20:58:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -88,6 +88,10 @@ s_lock(volatile slock_t *lock, const char *file, int line)
while (TAS(lock))
{
/* CPU-specific delay each time through the loop */
SPIN_DELAY();
/* Block the process every SPINS_PER_DELAY tries */
if (++spins > SPINS_PER_DELAY)
{
if (++delays > NUM_DELAYS)

23
src/include/storage/s_lock.h
View File

@ -24,6 +24,9 @@
* Tests if the lock is free. Returns TRUE if free, FALSE if locked.
* This does *not* change the state of the lock.
*
* void SPIN_DELAY(void)
* Delay operation to occur inside spinlock wait loop.
*
* Note to implementors: there are default implementations for all these
* macros at the bottom of the file. Check if your platform can use
* these or needs to override them.
@ -63,7 +66,7 @@
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.123 2003/12/23 22:15:07 tgl Exp $
* $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.124 2003/12/27 20:58:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -107,14 +110,28 @@ tas(volatile slock_t *lock)
{
register slock_t _res = 1;
/* Use a non-locking test before asserting the bus lock */
__asm__ __volatile__(
" cmpb $0,%1 \n"
" jne 1f \n"
" lock \n"
" xchgb %0,%1 \n"
"1: \n"
: "=q"(_res), "=m"(*lock)
: "0"(_res));
return (int) _res;
}
#define SPIN_DELAY() spin_delay()
static __inline__ void
spin_delay(void)
{
__asm__ __volatile__(
" rep; nop \n"
: : : "memory");
}
#endif /* __i386__ || __x86_64__ */
@ -708,6 +725,10 @@ extern int tas_sema(volatile slock_t *lock);
#define S_INIT_LOCK(lock) S_UNLOCK(lock)
#endif /* S_INIT_LOCK */
#if !defined(SPIN_DELAY)
#define SPIN_DELAY() ((void) 0)
#endif /* SPIN_DELAY */
#if !defined(TAS)
extern int tas(volatile slock_t *lock); /* in port/.../tas.s, or
* s_lock.c */