Commit 96567161 authored by Christian Ehrhardt's avatar Christian Ehrhardt Committed by Linus Torvalds

[PATCH] s390: Increase spinlock retry code performance

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: default avatarChristian Ehrhardt <ehrhardt@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 6a88231f
...@@ -2,8 +2,7 @@ ...@@ -2,8 +2,7 @@
* arch/s390/lib/spinlock.c * arch/s390/lib/spinlock.c
* Out of line spinlock code. * Out of line spinlock code.
* *
* S390 version * Copyright (C) IBM Corp. 2004, 2006
* Copyright (C) 2004 IBM Deutschland Entwicklung GmbH, IBM Corporation
* Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com) * Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
*/ */
...@@ -44,6 +43,8 @@ _raw_spin_lock_wait(raw_spinlock_t *lp, unsigned int pc) ...@@ -44,6 +43,8 @@ _raw_spin_lock_wait(raw_spinlock_t *lp, unsigned int pc)
_diag44(); _diag44();
count = spin_retry; count = spin_retry;
} }
if (__raw_spin_is_locked(lp))
continue;
if (_raw_compare_and_swap(&lp->lock, 0, pc) == 0) if (_raw_compare_and_swap(&lp->lock, 0, pc) == 0)
return; return;
} }
...@@ -56,6 +57,8 @@ _raw_spin_trylock_retry(raw_spinlock_t *lp, unsigned int pc) ...@@ -56,6 +57,8 @@ _raw_spin_trylock_retry(raw_spinlock_t *lp, unsigned int pc)
int count = spin_retry; int count = spin_retry;
while (count-- > 0) { while (count-- > 0) {
if (__raw_spin_is_locked(lp))
continue;
if (_raw_compare_and_swap(&lp->lock, 0, pc) == 0) if (_raw_compare_and_swap(&lp->lock, 0, pc) == 0)
return 1; return 1;
} }
...@@ -74,6 +77,8 @@ _raw_read_lock_wait(raw_rwlock_t *rw) ...@@ -74,6 +77,8 @@ _raw_read_lock_wait(raw_rwlock_t *rw)
_diag44(); _diag44();
count = spin_retry; count = spin_retry;
} }
if (!__raw_read_can_lock(rw))
continue;
old = rw->lock & 0x7fffffffU; old = rw->lock & 0x7fffffffU;
if (_raw_compare_and_swap(&rw->lock, old, old + 1) == old) if (_raw_compare_and_swap(&rw->lock, old, old + 1) == old)
return; return;
...@@ -88,6 +93,8 @@ _raw_read_trylock_retry(raw_rwlock_t *rw) ...@@ -88,6 +93,8 @@ _raw_read_trylock_retry(raw_rwlock_t *rw)
int count = spin_retry; int count = spin_retry;
while (count-- > 0) { while (count-- > 0) {
if (!__raw_read_can_lock(rw))
continue;
old = rw->lock & 0x7fffffffU; old = rw->lock & 0x7fffffffU;
if (_raw_compare_and_swap(&rw->lock, old, old + 1) == old) if (_raw_compare_and_swap(&rw->lock, old, old + 1) == old)
return 1; return 1;
...@@ -106,6 +113,8 @@ _raw_write_lock_wait(raw_rwlock_t *rw) ...@@ -106,6 +113,8 @@ _raw_write_lock_wait(raw_rwlock_t *rw)
_diag44(); _diag44();
count = spin_retry; count = spin_retry;
} }
if (!__raw_write_can_lock(rw))
continue;
if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0) if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0)
return; return;
} }
...@@ -118,6 +127,8 @@ _raw_write_trylock_retry(raw_rwlock_t *rw) ...@@ -118,6 +127,8 @@ _raw_write_trylock_retry(raw_rwlock_t *rw)
int count = spin_retry; int count = spin_retry;
while (count-- > 0) { while (count-- > 0) {
if (!__raw_write_can_lock(rw))
continue;
if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0) if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000) == 0)
return 1; return 1;
} }
......
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