From: Peter Zijlstra <peterz@infradead.org>
To: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mutex: have non-spinning mutexes on s390 by default
Date: Thu, 09 Apr 2009 18:53:51 +0200 [thread overview]
Message-ID: <1239296031.21985.28.camel@twins> (raw)
In-Reply-To: <20090409184834.7a0df7b2@osiris.boeblingen.de.ibm.com>
On Thu, 2009-04-09 at 18:48 +0200, Heiko Carstens wrote:
> 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>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
I was looking at how an monitor-wait could be used here, but that
appears non-trivial, there's two variables we're watching, lock->owner
and rq->curr, either could change.
Reducing that to 1 seems an interesting problem :-)
next prev parent reply other threads:[~2009-04-09 16:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-09 15:47 [PATCH] mutex: have non-spinning mutexes on s390 by default Heiko Carstens
2009-04-09 15:54 ` Peter Zijlstra
2009-04-09 16:14 ` Heiko Carstens
2009-04-09 16:48 ` Heiko Carstens
2009-04-09 16:53 ` Peter Zijlstra [this message]
2009-04-09 17:38 ` Peter Zijlstra
2009-04-09 17:50 ` Jeremy Fitzhardinge
2009-04-09 18:34 ` Peter Zijlstra
2009-04-09 18:12 ` [tip:core/urgent] " Heiko Carstens
2009-04-17 21:42 ` [PATCH] " Folkert van Heusden
2009-04-20 12:01 ` Heiko Carstens
2009-04-20 12:04 ` David Miller
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