Subject: Re: volano ~30% regression with 2.6.33-rc1 & -rc2
From: Mike Galbraith <efault@gmx.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Arjan van de Ven <arjan@infradead.org>, Lin Ming <ming.m.lin@intel.com>,
       lkml <linux-kernel@vger.kernel.org>,
       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
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	 <20100104044024.5390ff1c@infradead.org>
	 <1262609854.9734.56.camel@marge.simson.net>
	 <1262610123.6408.120.camel@laptop>
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Date: Mon, 04 Jan 2010 14:15:27 +0100
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On Mon, 2010-01-04 at 14:02 +0100, Peter Zijlstra wrote:
> On Mon, 2010-01-04 at 13:57 +0100, Mike Galbraith wrote:
> > On Mon, 2010-01-04 at 04:40 -0800, Arjan van de Ven wrote:
> > > On Mon, 04 Jan 2010 16:15:58 +0800
> > > Lin Ming <ming.m.lin@intel.com> wrote:
> > > 
> > > > Mike & Peter,
> > > > 
> > > > Compared with 2.6.32, volano has ~30% regression with 2.6.33-rc1 &
> > > > -rc2. Testing machine: Tigerton Xeon, 16cpus(4P/4Core), 16G memory
> > > 
> > > did this show up only on this cpu?
> > > (since this is a multi-core-without-shared-cache cpu, it could be that
> > > we get the topology wrong and think cores share cache where they don't)
> > 
> > My fault for using PREFER_SIBLING I guess.  However, I do wonder why in
> > the heck we set that at the CPU domain level.  Siblings lie northward.
> 
> Ah, PREFER_SIBLING means prefer sibling domain, not sibling thread. Its
> set at the CPU (really socket) level so make tasks spread over sockets
> first, so that there is no competition for the socket wide resources.

WRT the regression, would you prefer only the sched_fair.c hunk, and
maybe plunking the topology hunk in sched_devel, or both lines in one
patch, since ramp-up gain remains unrealized half of the time on Nehalem
and ilk.

> Your change is sane, but we really want a more extensive sched domain
> tree in the near future, reflecting the full machine topology.

Yeah.

	-Mike

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