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    SubjectRE: SCHED_RR and kernel threads
    Date
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    > From: Con Kolivas [mailto:kernel@kolivas.org] 
    > Stephen Warren wrote:
    > > It appears that during times of high application CPU usage, some
    > > *kernel* threads don't get to run.
    > > ...
    > > This appears to be due to the fact that the kernel threads are all
    > > SCHED_OTHER, so our SCHED_RR user-space application trumps them!
    >
    > Don't run your userspace at SCHED_RR? The kernel threads are
    > SCHED_NORMAL precisely for the reason that you wont get real time
    > performance if the kernel threads rear their ugly heads,
    > albeit rarely.

    We have actually set the kernel threads to priority SCHED_RR 50, and
    most user-space threads to SCHED_RR priority 50. Some critical
    user-space threads are above priority 50.

    Won't this allow the kernel and user space threads to co-operate nicely
    all the time?

    What is it specifically that will make kernel SCHED_RR threads cause
    non-real-time operation? If it's just a bunch of corner cases or odd
    conditions, we may be in an environment we can control so that doesn't
    happen...

    I guess we could have most threads stay at SCHED_NORMAL, and just make
    the few critical threads SCHED_RR, but I'm getting a lot of push-back on
    this, since it makes our thread API a lot more complex.

    --
    Stephen Warren, Software Engineer, NVIDIA, Fort Collins, CO
    swarren@nvidia.com http://www.nvidia.com/
    swarren@wwwdotorg.org http://www.wwwdotorg.org/pgp.html
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