linux-kernel - Re: Kernel v4.7-rc5 - performance degradation upto 40% after disabling and re-enabling a core

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Message-ID: <20160629095824.GW30921@twins.programming.kicks-ass.net>
Date:	Wed, 29 Jun 2016 11:58:24 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jirka Hladky <jhladky@...hat.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Kamil Kolakowski <kkolakow@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Jean-Pierre Lozi <jplozi@...ce.fr>,
	Alexandra Fedorova <sasha@....ubc.ca>,
	Baptiste Lepers <baptiste.lepers@...il.com>
Subject: Re: Kernel v4.7-rc5 - performance degradation upto 40% after
 disabling and re-enabling a core

On Wed, Jun 29, 2016 at 11:47:56AM +0200, Jirka Hladky wrote:
> Hi Peter,
> 
> I think Cluster on Die technology was introduced in Haswell generation. The
> server I'm using is equipped with 4x Intel E5-4610 v2 (Ivy Bridge). I have
> double checked the BIOS and there is no cluster on die setting.

Oh right, that's E5v3..

> The authors of the paper have reported the issue on AMD Bulldozer CPU which
> also does not have COD technology.

The Opteron 6272, which they use, is an Interlagos, that has something
similar in that each package contains two nodes.

And their patch touches exactly that part of the x86 topo setup, the
match_die() && !same_node() condition, IOW same package, different node.

That's not a path an Intel chip would trigger without COD support.