From 96567161de0ceed45cd2eb0e5380e3c797f5c0f4 Mon Sep 17 00:00:00 2001
From: Christian Ehrhardt <ehrhardt@de.ibm.com>
Date: Thu, 9 Mar 2006 17:33:49 -0800
Subject: [PATCH] [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: 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>
---
arch/s390/lib/spinlock.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index 60f80a4eed4e..b9b7958a226a 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c
@@ -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;
}