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

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Date:	Tue, 12 Jul 2016 11:04:54 +0200
From:	Jirka Hladky <jhladky@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
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

Hi Peter,

have you a chance to look into this? Is there anything I can do to
help you to fix it?

Thanks a lot!
Jirka


On Wed, Jun 29, 2016 at 11:58 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 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.