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[PATCH] s390: Increase spinlock retry code performance

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Currently the code tries up to spin_retry times to grab a lock using the cs
instruction.  The cs instruction has exclusive access to a memory region
and therefore invalidates the appropiate cache line of all other cpus.  If
there is contention on a lock this leads to cache line trashing.  This can
be avoided if we first check wether a cs instruction is likely to succeed
before the instruction gets actually executed.

Signed-off-by: Christian Ehrhardt <ehrhardt@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Christian Ehrhardt 2006-03-09 17:33:49 -08:00 committed by Linus Torvalds
parent 6a88231fc7
commit 96567161de
1 changed files with 13 additions and 2 deletions
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15
arch/s390/lib/spinlock.c
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@ -2,8 +2,7 @@
* arch/s390/lib/spinlock.c
* Out of line spinlock code.
*
* S390 version
* Copyright (C) 2004 IBM Deutschland Entwicklung GmbH, IBM Corporation
* Copyright (C) IBM Corp. 2004, 2006
* Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
*/
@ -44,6 +43,8 @@ _raw_spin_lock_wait(raw_spinlock_t *lp, unsigned int pc)
_diag44();
count = spin_retry;
}
if (__raw_spin_is_locked(lp))
continue;
if (_raw_compare_and_swap(&lp->lock, 0, pc) == 0)
return;
}
@ -56,6 +57,8 @@ _raw_spin_trylock_retry(raw_spinlock_t *lp, unsigned int pc)
int count = spin_retry;
while (count-- > 0) {
if (__raw_spin_is_locked(lp))
continue;
if (_raw_compare_and_swap(&lp->lock, 0, pc) == 0)
return 1;
}
@ -74,6 +77,8 @@ _raw_read_lock_wait(raw_rwlock_t *rw)
_diag44();
count = spin_retry;
}
if (!__raw_read_can_lock(rw))
continue;
old = rw->lock & 0x7fffffffU;
if (_raw_compare_and_swap(&rw->lock, old, old + 1) == old)
return;
@ -88,6 +93,8 @@ _raw_read_trylock_retry(raw_rwlock_t *rw)
int count = spin_retry;
while (count-- > 0) {
if (!__raw_read_can_lock(rw))
continue;
old = rw->lock & 0x7fffffffU;
if (_raw_compare_and_swap(&rw->lock, old, old + 1) == old)
return 1;
@ -106,6 +113,8 @@ _raw_write_lock_wait(raw_rwlock_t *rw)
_diag44();
count = spin_retry;
}
if (!__raw_write_can_lock(rw))
continue;
if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0)
return;
}
@ -118,6 +127,8 @@ _raw_write_trylock_retry(raw_rwlock_t *rw)
int count = spin_retry;
while (count-- > 0) {
if (!__raw_write_can_lock(rw))
continue;
if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0)
return 1;
}