linux-kernel - Re: [PATCH] mutex: have non-spinning mutexes on s390 by default

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Message-ID: <20090417214212.GG10554@vanheusden.com>
Date:	Fri, 17 Apr 2009 23:42:12 +0200
From:	Folkert van Heusden <folkert@...heusden.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mutex: have non-spinning mutexes on s390 by default

> 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.

Hmmm. Wouldn't this be a change that applies to ibm system p as wel?
E.g. with linux in an lpar.


Folkert van Heusden

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