linux-kernel - Re: Scheduler regression from caffcdd8d27ba78730d5540396ce72ad022aff2c

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Date:	Fri, 18 Jul 2014 18:16:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Bruno Wolff III <bruno@...ff.to>
Cc:	Dietmar Eggemann <dietmar.eggemann@....com>,
	Josh Boyer <jwboyer@...hat.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Scheduler regression from
 caffcdd8d27ba78730d5540396ce72ad022aff2c

On Fri, Jul 18, 2014 at 04:50:40PM +0200, Peter Zijlstra wrote:
> On Fri, Jul 18, 2014 at 04:16:48PM +0200, Peter Zijlstra wrote:
> > On Fri, Jul 18, 2014 at 08:01:26AM -0500, Bruno Wolff III wrote:
> > > build_sched_domain: cpu: 0 level: SMT cpu_map: 0-3 tl->mask: 0,2
> > > [    0.254433] build_sched_domain: cpu: 0 level: MC cpu_map: 0-3 tl->mask: 0
> > > [    0.254516] build_sched_domain: cpu: 0 level: DIE cpu_map: 0-3 tl->mask: 0-3
> > > [    0.254600] build_sched_domain: cpu: 1 level: SMT cpu_map: 0-3 tl->mask: 1,3
> > > [    0.254683] build_sched_domain: cpu: 1 level: MC cpu_map: 0-3 tl->mask: 1
> > > [    0.254766] build_sched_domain: cpu: 1 level: DIE cpu_map: 0-3 tl->mask: 0-3
> > > [    0.254850] build_sched_domain: cpu: 2 level: SMT cpu_map: 0-3 tl->mask: 0,2
> > > [    0.254932] build_sched_domain: cpu: 2 level: MC cpu_map: 0-3 tl->mask: 2
> > > [    0.255005] build_sched_domain: cpu: 2 level: DIE cpu_map: 0-3 tl->mask: 0-3
> > > [    0.255091] build_sched_domain: cpu: 3 level: SMT cpu_map: 0-3 tl->mask: 1,3
> > > [    0.255176] build_sched_domain: cpu: 3 level: MC cpu_map: 0-3 tl->mask: 3
> > > [    0.255260] build_sched_domain: cpu: 3 level: DIE cpu_map: 0-3 tl->mask: 0-3
> > 
> > *blink*...
> > 
> > That's, shall we say, unexpected. Let me ponder that a bit. HPA any clue
> > why a machine might report such a weird topology? AFAIK threads _always_
> > share cache.  So how can cpu_coregroup_mask be a subset (instead of a
> > superset) of topology_thread_cpumask?
> > 
> > Let me go stare at the x86 topology mask setup code.
> 
> Possibly something like so, but I'm not too sure. Anybody?

OK, Borislav says topoext is AMD only, so that's not the problem. In
which case the problem must be that cpu_llc_id is wrong.

This gets set in init_intel_cacheinfo() but that's hurting my brain for
the moment. There's plenty P4 specific cruft in there though.
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