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    SubjectRe: commit e9e9250b: sync wakeup bustage when waker is an RT task
    On Mon, 2010-05-31 at 13:56 +0200, Peter Zijlstra wrote:
    > On Sun, 2010-05-16 at 09:21 +0200, Mike Galbraith wrote:
    > > sched: RT waker sync wakeup bugfix
    > >
    > > An RT waker's weight is not on the runqueue, but we try to subrtact it anyway
    > > in the sync wakeup case, sending this_load negative. This leads to affine
    > > wakeup failure in cases where it should succeed. This was found while testing
    > > an PREEMPT_RT kernel with lmbench's lat_udp. In a PREEMPT_RT kernel, softirq
    > > threads act as a ~proxy for the !RT buddy. Approximate !PREEMPT_RT sync wakeup
    > > behavior by looking at the buddy instead, and subtracting the maximum task weight
    > > that will not send this_load negative.
    > Does the below work?

    Had to make a dinky adjustment for x86-tip-rt33, but yeah, the horrid
    latencies are gone. (hm, skinnier than expected too)


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