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    SubjectRe: [rfc][patch] select_idle_sibling() inducing bouncing on westmere
    On Sat, May 26, 2012 at 09:29:24AM +0200, Peter Zijlstra wrote:
    > On Sat, 2012-05-26 at 08:37 +0200, Mike Galbraith wrote:
    >
    > > Ew. 3.4 went broke for Q6600, and performance went... far far away.
    > >
    > > [ 0.200057] CPU0 attaching sched-domain:
    > > [ 0.204016] domain 0: span 0-3 level MC
    > > [ 0.208015] groups: 0 1 2 3
    > > [ 0.210970] CPU1 attaching sched-domain:
    > > [ 0.212014] domain 0: span 0-3 level MC
    > > [ 0.216016] groups: 1 2 3 0
    > > [ 0.220016] CPU2 attaching sched-domain:
    > > [ 0.224015] domain 0: span 0-3 level MC
    > > [ 0.228016] groups: 2 3 0 1
    > > [ 0.232015] CPU3 attaching sched-domain:
    > > [ 0.236016] domain 0: span 0-3 level MC
    > > [ 0.240017] groups: 3 0 1 2
    >
    >
    > Oh yikes, I guess I wrecked
    > arch/x86/kernel/smpboot.c:cpu_coregroup_mask() in
    > 8e7fbcbc22c12414bcc9dfdd683637f58fb32759.
    >
    > That should very much always return llc mask, I just got that AMD case
    > confused. It looks like it should look like:
    >
    >
    > const struct cpumask *cpu_coregroup_mask(int cpu)
    > {
    > return cpu_llc_mask(cpu);
    > }
    >
    > And the AMD_DCM check was just to undo powersavings damage on
    > Magny-Cours or somesuch.

    IIRC returning cpu_core_mask() could even cause a panic in the
    scheduler, because the hierarchy of scheduling groups/domains was
    broken.

    > Andreas?

    Returning cpu_llc_mask is the right thing to do on AMD.



    Andreas




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