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    SubjectRe: [PATCH] block: strip out locking optimization in put_io_context()
    On Thu, Feb 9, 2012 at 9:59 AM, Tejun Heo <tj@kernel.org> wrote:
    >
    > * What exactly is the test and what do you measure?  What does "12%
    >  regression" mean?  Is it wallclock time or CPU time?  If it's CPU
    >  time, does systime increase dominate the regression?

    Shaohua, it might be interesting to see a profile of the bad case.

    Now, quite often these kinds of things don't show anything at all -
    it's just due to cache issues and there's no obvious "we hold spinlock
    X for 15 seconds total". But if it's actual lock contention rather
    than just "more scheduling of worker threads", it should show up in
    the profile quite clearly.

    That said, I do think the RCU approach is the right one. The whole
    delayed deallocation (and the replacement patch with rwlocks) really
    smells like "badly done RCU-like behavior" to me.

    Linus
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