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SubjectRe: Scheduler grouping failure; division by zero in select_task_rq_fair

* Ben Hutchings <ben@decadent.org.uk> wrote:

> On Mon, Nov 29, 2010 at 12:50:25PM +0100, Peter Zijlstra wrote:
> > On Sun, 2010-11-28 at 20:14 +0000, Ben Hutchings wrote:
> >
> > > [ 0.856002] Pid: 2, comm: kthreadd Not tainted 2.6.32-5-amd64 #1 W1100z/2100z
> >
> > What's in that kernel? is that simply the latest .32-stable?
>
> No, we have quite a few backported driver features and some bug fixes
> that aren't in stable yet. No scheduler or topology changes except
> reverting 669c55e9f99b90e46eaa0f98a67ec53d46dc969a for ABI reasons
> (which I guess we don't actually need to do).
>
> > > [ 0.536554] CPU0 attaching sched-domain:
> > > [ 0.540004] domain 0: span 0-1 level MC
> > > [ 0.548002] groups: 0 1
> > > [ 0.560003] domain 1: span 0-3 level NODE
> > > [ 0.568002] groups:
> > > [ 0.574179] ERROR: domain->cpu_power not set
> > > [ 0.576002]
> > > [ 0.580002] ERROR: groups don't span domain->span
> > > [ 0.584004] CPU1 attaching sched-domain:
> > > [ 0.588007] domain 0: span 0-1 level MC
> > > [ 0.596002] groups: 1 0 (cpu_power = 1023)
> > > [ 0.612002] ERROR: parent span is not a superset of domain->span
> > > [ 0.616003] domain 1: span 1-3 level CPU
> > > [ 0.624002] groups: 1 (cpu_power = 2048) 2-3 (cpu_power = 2048)
> > > [ 0.644003] domain 2: span 0-3 level NODE
> > > [ 0.652004] groups: 1-3 (cpu_power = 4096)
> > > [ 0.668002] ERROR: domain->cpu_power not set
> > > [ 0.672002]
> > > [ 0.676002] ERROR: groups don't span domain->span
> > > [ 0.680004] CPU2 attaching sched-domain:
> > > [ 0.684003] domain 0: span 2-3 level MC
> > > [ 0.692003] groups: 2 3
> > > [ 0.704003] domain 1: span 1-3 level CPU
> > > [ 0.712003] groups: 2-3 (cpu_power = 2048) 1 (cpu_power = 2048)
> > > [ 0.736003] domain 2: span 0-3 level NODE
> > > [ 0.744003] groups: 1-3 (cpu_power = 4096)
> > > [ 0.760003] ERROR: domain->cpu_power not set
> > > [ 0.764003]
> > > [ 0.768003] ERROR: groups don't span domain->span
> > > [ 0.772004] CPU3 attaching sched-domain:
> > > [ 0.776003] domain 0: span 2-3 level MC
> > > [ 0.784003] groups: 3 2
> > > [ 0.794183] domain 1: span 1-3 level CPU
> > > [ 0.800003] groups: 2-3 (cpu_power = 2048) 1 (cpu_power = 2048)
> > > [ 0.822183] domain 2: span 0-3 level NODE
> > > [ 0.828003] groups: 1-3 (cpu_power = 4096)
> > > [ 0.842180] ERROR: domain->cpu_power not set
> > > [ 0.844003]
> > > [ 0.848003] ERROR: groups don't span domain->span
> >
> > Hrm that smells like the architecture topology setup is wrecked, looks
> > like the NUMA setup is bonkers.
> [...]
>
> Right, that's what I thought. Question is whether the topology setup
> code should fix this up or whether the schedular init should (as it
> appears to have done before 2.6.32).

We definitely want to robustify scheduler init code to not crash and to (if
possible) print a warning about the borkage.

Thanks,

Ingo


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