From 36cd3c9f925b9307236505ae7ad1ad7ac4d4357c Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Thu, 9 Apr 2009 18:48:34 +0200 Subject: mutex: have non-spinning mutexes on s390 by default Impact: performance regression fix for s390 The adaptive spinning mutexes will not always do what one would expect on virtualized architectures like s390. Especially the cpu_relax() loop in mutex_spin_on_owner might hurt if the mutex holding cpu has been scheduled away by the hypervisor. We would end up in a cpu_relax() loop when there is no chance that the state of the mutex changes until the target cpu has been scheduled again by the hypervisor. For that reason we should change the default behaviour to no-spin on s390. We do have an instruction which allows to yield the current cpu in favour of a different target cpu. Also we have an instruction which allows us to figure out if the target cpu is physically backed. However we need to do some performance tests until we can come up with a solution that will do the right thing on s390. Signed-off-by: Heiko Carstens Acked-by: Peter Zijlstra Cc: Martin Schwidefsky Cc: Christian Borntraeger LKML-Reference: <20090409184834.7a0df7b2@osiris.boeblingen.de.ibm.com> Signed-off-by: Ingo Molnar --- kernel/mutex.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/mutex.c b/kernel/mutex.c index 5d79781..507cf2b 100644 --- a/kernel/mutex.c +++ b/kernel/mutex.c @@ -148,7 +148,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, preempt_disable(); mutex_acquire(&lock->dep_map, subclass, 0, ip); -#if defined(CONFIG_SMP) && !defined(CONFIG_DEBUG_MUTEXES) +#if defined(CONFIG_SMP) && !defined(CONFIG_DEBUG_MUTEXES) && \ + !defined(CONFIG_HAVE_DEFAULT_NO_SPIN_MUTEXES) /* * Optimistic spinning. * -- cgit v1.1