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

arch/s390/lib/spinlock.c

+13 −2
Original line number Diff line number Diff line
@@ -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;

	}