linux-kernel - Re: aim7 scalability issue on 4 socket machine

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Date:	Fri, 18 Sep 2009 00:05:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Andi Kleen <andi@...stfloor.org>,
	"lee.schermerhorn@...com" <lee.schermerhorn@...com>,
	stable@...nel.org
Subject: Re: aim7 scalability issue on 4 socket machine

On Fri, 18 Sep 2009 07:53:58 +0100 (BST) Hugh Dickins <hugh.dickins@...cali.co.uk> wrote:

> On Thu, 17 Sep 2009, Andrew Morton wrote:
> > On Fri, 18 Sep 2009 10:02:19 +0800 "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com> wrote:
> > > > 
> > > > So, Yanmin, please retest with http://lkml.org/lkml/2009/9/13/25
> > > > and let us know if that works as well for you - thanks.
> > > I tested Lee's patch and it does fix the issue.
> 
> Thanks for checking and reporting back, Yanmin.
> 
> > 
> > Do we think we should cook up something for -stable?
> 
> Gosh, I laughed at Lee (sorry!) for suggesting it for -stable:
> is stable really for getting a better number out of a benchmark?
> 
> I'd have thought the next release is the right place for that; but
> I've no problem if you guys and the stable guys agree it's appropriate.
> 
> > 
> > Either this is a regression or the workload is particularly obscure. 
> 
> I've not cross-checked descriptions, but assume Lee was actually
> testing on exactly the same kind of upcoming Nehalem as Yanmin, and
> that machine happens to have characteristics which show up badly here.
> 
> > 
> > aim7 is sufficiently non-obscure to make me wonder what's happened here?
> 
> Not a regression, just the onward march of new hardware, I think.
> Could easily be other such things in other places with other tests.
> 

Well, it comes down to the question "what is -stable for".

If you take it as "bugfixed version of the 2.6.x kernel" then no,
speedups aren't appropriate.

If you consider -stable to be "something distros, etc will use" then
yes, perhaps we serve those consumers better by including fairly major
efficiency improvements.

I suspect most consumers of -stable would prefer the latter approach,
as long as we don't go nuts.
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