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    SubjectRe: [PATCH [RT] 10/14] adjust pi_lock usage in wakeup
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    On Thu, 2008-02-21 at 11:48 -0500, Steven Rostedt wrote:
    > On Thu, 21 Feb 2008, Gregory Haskins wrote:
    >
    > > From: Peter W.Morreale <pmorreale@novell.com>
    > >
    > > In wakeup_next_waiter(), we take the pi_lock, and then find out whether
    > > we have another waiter to add to the pending owner. We can reduce
    > > contention on the pi_lock for the pending owner if we first obtain the
    > > pointer to the next waiter outside of the pi_lock.
    > >
    > > This patch adds a measureable increase in throughput.
    >
    > I see how this may decrease contention (slightly less time in holding the
    > pi_lock). But, please, when stating something like: "adds a measurable
    > increase in throughput", show the benchmark numbers.
    >
    > -- Steve
    >

    Approximately 3% to the dbench benchmark we used.

    My "standard" sanity check was to mount a ramfs filesystem and execute:

    dbench -t 10 30

    five times and generate an average from the reported "Throughput"
    numbers displayed by the runs.

    dbench was chosen merely because of the contention on dcache_lock.

    Best,
    -PWM




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