linux-kernel - Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets

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Date:	Wed, 26 Sep 2012 19:15:41 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>,
	Nikolay Ulyanitsky <lystor@...il.com>,
	linux-kernel@...r.kernel.org,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to
 3.6-rc5 on AMD chipsets - bisected

On Tue, Sep 25, 2012 at 07:22:22PM -0700, Linus Torvalds wrote:
> So I'm sure there are architecture differences (where HT in particular
> probably changes optimal scheduling strategy, although I'd expect
> the bulldozer approach to not be *that*different - but I don't know
> if BD shows up as "HT siblings" or not, so dissimilar topology
> interpretation may make it *look* very different).

Right, those cores sharing an L2 are thread siblings on BD:

$ grep . /sys/devices/system/cpu/cpu0/topology/*
/sys/devices/system/cpu/cpu0/topology/core_id:0
/sys/devices/system/cpu/cpu0/topology/core_siblings:ff
/sys/devices/system/cpu/cpu0/topology/core_siblings_list:0-7
/sys/devices/system/cpu/cpu0/topology/physical_package_id:0
/sys/devices/system/cpu/cpu0/topology/thread_siblings:03
/sys/devices/system/cpu/cpu0/topology/thread_siblings_list:0-1

much like HT siblings on this single-socket Sandybridge: 

$ grep . /sys/devices/system/cpu/cpu0/topology/*
/sys/devices/system/cpu/cpu0/topology/core_id:0
/sys/devices/system/cpu/cpu0/topology/core_siblings:ff
/sys/devices/system/cpu/cpu0/topology/core_siblings_list:0-7
/sys/devices/system/cpu/cpu0/topology/physical_package_id:0
/sys/devices/system/cpu/cpu0/topology/thread_siblings:11
/sys/devices/system/cpu/cpu0/topology/thread_siblings_list:0,4

Although I don't know whether those thread siblings on this SB box are
actual HT siblings, sharing almost all resources, judging by the core
ids.

-- 
Regards/Gruss,
Boris.
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