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    SubjectRe: [PATCH] sched: avoid large irq-latencies in smp-balancing
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    On Wed, 2007-11-07 at 17:10 -0500, Steven Rostedt wrote:
    > >
    > > It would be nice if sched_nr_migrate didn't exist, really. It's hard to
    > > imagine anyone wanting to tweak it, apart from developers.
    >
    > I'm not so sure about that. It is a tunable for RT. That is we can tweak
    > this value to be smaller if we don't like the latencies it gives us.
    >
    > This is one of those things that sacrifices performance for latency.
    > The higher the number, the better it can spread tasks around, but it
    > also causes large latencies.
    >
    > I've just included this patch into 2.6.23.1-rt11 and it brought down an
    > unbounded latency to just 42us. (previously we got into the
    > milliseconds!).
    >
    > Perhaps when this feature matures, we can come to a good defined value
    > that would be good for all. But until then, I recommend keeping this a
    > tunable.


    Why not use the latency-expectation infrastructure?

    Iterate under lock until (or before...) the system global latency is
    respected.


    - Eric

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