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    SubjectRe: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR
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    On 7/23/20 2:47 PM, peterz@infradead.org wrote:
    > On Thu, Jul 23, 2020 at 02:32:36PM -0400, Waiman Long wrote:
    >> BTW, do you have any comment on my v2 lock holder cpu info qspinlock patch?
    >> I will have to update the patch to fix the reported 0-day test problem, but
    >> I want to collect other feedback before sending out v3.
    > I want to say I hate it all, it adds instructions to a path we spend an
    > aweful lot of time optimizing without really getting anything back for
    > it.

    It does add some extra instruction that may slow it down slightly, but I
    don't agree that it gives nothing back. The cpu lock holder information
    can be useful in analyzing crash dumps and in some debugging situation.
    I think it can be useful in RHEL for this readon. How about an x86
    config option to allow distros to decide if they want to have it
    enabled? I will make sure that it will have no performance degradation
    if the option is not enabled.

    Cheers,
    Longman


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