linux-kernel - Re: Scheduler grouping failure; division by zero in select_task_rq

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Date:	Mon, 29 Nov 2010 19:06:05 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Peter Zijlstra <peterz@...radead.org>, Frede_Feuerstein@....net,
	603229@...s.debian.org, LKML <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: Scheduler grouping failure; division by zero in
 select_task_rq_fair


* Ben Hutchings <ben@...adent.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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