linux-kernel - Re: [rfc][patch] select_idle_sibling() inducing bouncing on westmere

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Message-ID: <1338017364.14636.9.camel@twins>
Date:	Sat, 26 May 2012 09:29:24 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <efault@....de>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Paul Turner <pjt@...gle.com>,
	Arjan Van De Ven <arjan@...ux.intel.com>,
	Andreas Herrmann <andreas.herrmann3@....com>
Subject: Re: [rfc][patch] select_idle_sibling() inducing bouncing on westmere

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.

Andreas?
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