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    SubjectRe: commit e9e9250b: sync wakeup bustage when waker is an RT task
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    On Sat, 2010-05-15 at 13:57 +0200, Mike Galbraith wrote:
    > Hi Peter,
    >
    > This commit excluded RT tasks from rq->load, was that intentional? The
    > comment in struct rq states that load reflects *all* tasks, but since
    > this commit, that's no longer true.

    Right, because a static load value does not accurately reflect a RT task
    which can run as long as it pretty well pleases. So instead we measure
    the time spend running !fair tasks and scale down the cpu_power
    proportionally.

    > Looking at lmbench lat_udp in a PREEMPT_RT kernel, I noticed that
    > wake_affine() is failing for sync wakeups when it should not. It's
    > doing so because the waker in this case is an RT kernel thread
    > (sirq-net-rx) - we subtract the sync waker's weight, when it was never
    > added in the first place, resulting in this_load going gaga. End result
    > is quite high latency numbers due to tasks jabbering cross-cache.
    >
    > If the exclusion was intentional, I suppose I can do a waker class check
    > in wake_affine() to fix it.

    So basically make all RT wakeups sync?



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