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    SubjectRe: [PATCH] mutex: have non-spinning mutexes on s390 by default
    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 <>
    > 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 <>

    Acked-by: Peter Zijlstra <>

    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 :-)

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      Last update: 2009-04-09 18:55    [W:0.047 / U:1.732 seconds]
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