Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

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

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

arch/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -109,3 +109,6 @@ config HAVE_CLK 


config HAVE_DMA_API_DEBUG

	bool



config HAVE_DEFAULT_NO_SPIN_MUTEXES

	bool

arch/s390/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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

kernel/mutex.c

+2 −1
Original line number Diff line number Diff line
@@ -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.

	 *