Commit 36cd3c9f authored by Heiko Carstens's avatar Heiko Carstens Committed by Ingo Molnar

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: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: default avatarPeter 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: default avatarIngo Molnar <mingo@elte.hu>
parent 022624a7
......@@ -109,3 +109,6 @@ config HAVE_CLK
config HAVE_DMA_API_DEBUG
bool
config HAVE_DEFAULT_NO_SPIN_MUTEXES
bool
......@@ -82,6 +82,7 @@ config S390
select USE_GENERIC_SMP_HELPERS if SMP
select HAVE_SYSCALL_WRAPPERS
select HAVE_FUNCTION_TRACER
select HAVE_DEFAULT_NO_SPIN_MUTEXES
select HAVE_OPROFILE
select HAVE_KPROBES
select HAVE_KRETPROBES
......
......@@ -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.
*
......
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