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    SubjectRe: [PATCH] sched: fair scheduler should not resched rt tasks

    On Sat, 11 Oct 2008, Peter Zijlstra wrote:

    > On Sat, 2008-10-11 at 03:01 -0400, Steven Rostedt wrote:
    > > Using ftrace, I noticed latencies in real-time tasks where they were
    > > needlessly calling schedule due to sched_fair sending out time slices.
    > >
    > > This patch prevents a call to resched_task by the sched fair class if
    > > the task it wants to reschedule is an rt task.
    > Right, thats not a good thing, however this patch looks wrong, we should
    > never call hrtick_start_fair() on a rt task to begin with.

    Great! I don't care which way we fix this. This was making noticeable
    latencies against rt tasks.

    > The way I can see that happening is through enqueue/dequeue_task_fair()
    > where we want to re-programm the hrtick because nr_running changes (and
    > thus the current tasks desired runtime).

    My original patch was more like this one, but I wasn't sure if I was
    skipping any calculations that were assumed to be made. Thus, I wrote the
    bare minimum and sent it out CC'ing the experts. Looks like my plan worked

    -- Steve

    > Signed-off-by: Peter Zijlstra <>

    Acked-by: Steven Rostedt <>

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      Last update: 2008-10-11 15:57    [W:0.019 / U:180.908 seconds]
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