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Commit9907b97

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Don't use a non-locked pre-test of the spinlock on x86_64 machines.
The pre-test has been shown to be a big loss on Opterons and at best awash on EM64T.
1 parent0cc0d08 commit9907b97

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1 file changed

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1 file changed

+50
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‎src/include/storage/s_lock.h

Lines changed: 50 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -66,7 +66,7 @@
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* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.140 2005/08/29 00:41:34 tgl Exp $
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* $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.141 2005/10/11 20:01:30 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -108,7 +108,7 @@
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*/
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#if defined(__i386__)|| defined(__x86_64__)/* AMD Opteron */
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#ifdef__i386__
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#defineHAS_TEST_AND_SET
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typedefunsignedcharslock_t;
@@ -120,7 +120,11 @@ tas(volatile slock_t *lock)
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{
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registerslock_t_res=1;
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123-
/* Use a non-locking test before asserting the bus lock */
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/*
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* Use a non-locking test before asserting the bus lock. Note that the
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* extra test appears to be a small loss on some x86 platforms and a small
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* win on others; it's by no means clear that we should keep it.
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*/
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__asm__ __volatile__(
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"cmpb$0,%1\n"
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"jne1f\n"
@@ -165,7 +169,49 @@ spin_delay(void)
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" rep; nop\n");
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}
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168-
#endif/* __i386__ || __x86_64__ */
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#endif/* __i386__ */
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#ifdef__x86_64__/* AMD Opteron, Intel EM64T */
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#defineHAS_TEST_AND_SET
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typedefunsignedcharslock_t;
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#defineTAS(lock) tas(lock)
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static __inline__int
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tas(volatileslock_t*lock)
184+
{
185+
registerslock_t_res=1;
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/*
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* On Opteron, using a non-locking test before the locking instruction
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* is a huge loss. On EM64T, it appears to be a wash or small loss,
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* so we needn't bother to try to distinguish the sub-architectures.
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*/
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__asm__ __volatile__(
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"lock\n"
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"xchgb%0,%1\n"
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:"+q"(_res),"+m"(*lock)
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:
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:"memory","cc");
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return (int)_res;
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}
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#defineSPIN_DELAY() spin_delay()
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static __inline__void
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spin_delay(void)
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{
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/*
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* Adding a PAUSE in the spin delay loop is demonstrably a no-op on
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* Opteron, but it may be of some use on EM64T, so we keep it.
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*/
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__asm__ __volatile__(
211+
" rep; nop\n");
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}
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#endif/* __x86_64__ */
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#if defined(__ia64__)|| defined(__ia64)

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