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    SubjectRe: BFS vs. mainline scheduler benchmarks and measurements

    * Jens Axboe <jens.axboe@oracle.com> wrote:

    > On Tue, Sep 08 2009, Peter Zijlstra wrote:
    > > On Tue, 2009-09-08 at 11:13 +0200, Jens Axboe wrote:
    > > > And here's a newer version.
    > >
    > > I tinkered a bit with your proglet and finally found the
    > > problem.
    > >
    > > You used a single pipe per child, this means the loop in
    > > run_child() would consume what it just wrote out until it got
    > > force preempted by the parent which would also get woken.
    > >
    > > This results in the child spinning a while (its full quota) and
    > > only reporting the last timestamp to the parent.
    >
    > Oh doh, that's not well thought out. Well it was a quick hack :-)
    > Thanks for the fixup, now it's at least usable to some degree.

    What kind of latencies does it report on your box?

    Our vanilla scheduler default latency targets are:

    single-core: 20 msecs
    dual-core: 40 msecs
    quad-core: 60 msecs
    opto-core: 80 msecs

    You can enable CONFIG_SCHED_DEBUG=y and set it directly as well via
    /proc/sys/kernel/sched_latency_ns:

    echo 10000000 > /proc/sys/kernel/sched_latency_ns

    Ingo


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