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authorHeiko Carstens <heiko.carstens@de.ibm.com>2009-04-09 18:48:34 +0200
committerIngo Molnar <mingo@elte.hu>2009-04-09 19:28:24 +0200
commit36cd3c9f925b9307236505ae7ad1ad7ac4d4357c (patch)
treed9be68502d0f11b2259427e9ee8320891367143c /kernel/mutex.c
parent022624a758dc9489388a99ad29577b4c8c09237c (diff)
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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 <heiko.carstens@de.ibm.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> LKML-Reference: <20090409184834.7a0df7b2@osiris.boeblingen.de.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/mutex.c')
-rw-r--r--kernel/mutex.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 5d79781394a..507cf2b5e9f 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.
*