Messages in this thread Patch in this message | | | Date | Thu, 9 Apr 2009 18:48:34 +0200 | From | Heiko Carstens <> | Subject | Re: [PATCH] mutex: have non-spinning mutexes on s390 by default |
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Updated Patch below:
Subject: [PATCH] mutex: have non-spinning mutexes on s390 by default
From: Heiko Carstens <heiko.carstens@de.ibm.com>
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.
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> --- arch/Kconfig | 3 +++ arch/s390/Kconfig | 1 + kernel/mutex.c | 3 ++- 3 files changed, 6 insertions(+), 1 deletion(-)
Index: linux-2.6/arch/Kconfig =================================================================== --- linux-2.6.orig/arch/Kconfig +++ linux-2.6/arch/Kconfig @@ -109,3 +109,6 @@ config HAVE_CLK config HAVE_DMA_API_DEBUG bool + +config HAVE_DEFAULT_NO_SPIN_MUTEXES + bool Index: linux-2.6/arch/s390/Kconfig =================================================================== --- linux-2.6.orig/arch/s390/Kconfig +++ linux-2.6/arch/s390/Kconfig @@ -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 Index: linux-2.6/kernel/mutex.c =================================================================== --- linux-2.6.orig/kernel/mutex.c +++ linux-2.6/kernel/mutex.c @@ -148,7 +148,8 @@ __mutex_lock_common(struct mutex *lock, 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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