Messages in this thread |  | | | Subject | Re: [PATCH] mutex: have non-spinning mutexes on s390 by default | | From | Peter Zijlstra <> | | Date | Thu, 09 Apr 2009 17:54:56 +0200 |
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On Thu, 2009-04-09 at 17:47 +0200, Heiko Carstens wrote: > 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. > Until then make the old behaviour default for us. > > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> > Cc: Ingo Molnar <mingo@elte.hu> > Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> > --- > arch/Kconfig | 3 +++ > arch/s390/Kconfig | 1 + > kernel/sched_features.h | 4 ++++ > 3 files changed, 8 insertions(+) > > 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/sched_features.h > =================================================================== > --- linux-2.6.orig/kernel/sched_features.h > +++ linux-2.6/kernel/sched_features.h > @@ -14,4 +14,8 @@ SCHED_FEAT(LB_WAKEUP_UPDATE, 1) > SCHED_FEAT(ASYM_EFF_LOAD, 1) > SCHED_FEAT(WAKEUP_OVERLAP, 0) > SCHED_FEAT(LAST_BUDDY, 1) > +#ifdef CONFIG_HAVE_DEFAULT_NO_SPIN_MUTEXES > +SCHED_FEAT(OWNER_SPIN, 0) > +#else > SCHED_FEAT(OWNER_SPIN, 1) > +#endif
Hmm, I'd rather have you'd make the whole block in __mutex_lock_common go away on that CONFIG thingy.
Would be nice though to get something working on s390, does it have a monitor wait like ins where it can properly sleep so that another virtual host can run?
If so, we could possibly do a monitor wait on the lock owner field instead of spinning.
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