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    SubjectRe: CPU scheduler weirdness?
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    On Wed, 2009-08-19 at 14:34 +0200, Marton Balint wrote:
    >
    > On Wed, 19 Aug 2009, Peter Zijlstra wrote:
    >
    > > On Wed, 2009-08-19 at 14:01 +0200, Marton Balint wrote:
    > >> On Wed, 19 Aug 2009, Peter Zijlstra wrote:
    > >>> On Tue, 2009-08-18 at 21:49 +0200, Marton Balint wrote:
    > >>>
    > >>>> In the meantime, I was able to create a tiny C program which always
    > >>>> succesfully reproduces the bug. It's basically an endless loop which does
    > >>>> not stop while the process is running on the last CPU core. The program
    > >>>> creates multiple instances of itself, to be able to keep all of the CPU
    > >>>> cores busy. After 1 second, the processes running on other than the last
    > >>>> CPU core die, the processes running on the last CPU core remain stuck
    > >>>> there...
    > >>>>
    > >>>> I tested it on my dual core system, if someone could test it on a quad
    > >>>> core and report back that would probably be useful.
    > >>>>
    > >>>> Usage: ./schedtest <number of CPU cores>
    > >>>>
    > >>>> And don't forget to kill the stuck processes after using the program! :)
    > >>>
    > >>> So what's the bug? Sure one task will stay on the cpu, and because there
    > >>> is no contention it doesn't get migrated, and therefore won't quit,
    > >>> how's that a problem?
    > >>
    > >> Problem is that more than one processes remain on that CPU core, and none
    > >> of them get migrated to other (idle) cores. I tested it with my E8400
    > >> processor and 2.6.31-rc5-git3 kernel.
    > >
    > > Only one remains here.. on a c2q running 2.6.31-rc6-tip
    > >
    > > Do you have a .config handy?
    > >
    >
    > Yes it's in my original post:
    >
    > http://marc.info/?l=linux-kernel&m=125012584709800&w=2

    Right you are,.. so I build a kernel with the cgroup scheduler in and
    tested it on a dual-core opteron machine, but I can't seem to reproduce
    this.

    Are you using cgroups in any way, or do you simply have it enabled in
    your config?



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