From: Christian Ehrhardt <[email protected]>
[patch 1/2] 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 <[email protected]>
Signed-off-by: Martin Schwidefsky <[email protected]>
---
arch/s390/lib/spinlock.c | 15 +++++++++++++--
1 files changed, 13 insertions(+), 2 deletions(-)
diff -urpN linux-2.6/arch/s390/lib/spinlock.c linux-2.6-patched/arch/s390/lib/spinlock.c
--- linux-2.6/arch/s390/lib/spinlock.c 2006-03-03 18:52:23.000000000 +0100
+++ linux-2.6-patched/arch/s390/lib/spinlock.c 2006-03-03 18:53:20.000000000 +0100
@@ -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 ([email protected])
*/
@@ -44,6 +43,8 @@ _raw_spin_lock_wait(raw_spinlock_t *lp,
_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 *
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 *r
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;
}