linux-kernel - Re: [PATCH 00/27] Latest numa/core release, v16

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Message-ID: <20121121172046.GA28975@gmail.com>
Date:	Wed, 21 Nov 2012 18:20:46 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Rientjes <rientjes@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 00/27] Latest numa/core release, v16


* Ingo Molnar <mingo@...nel.org> wrote:

> This is an entirely valid line of inquiry IMO.

Btw., what I did was to simply look at David's profile on the 
regressing system and I compared it to the profile I got on a 
pretty similar (but unfortunately not identical and not 
regressing) system. I saw 3 differences:

 - the numa emulation faults
 - the higher TLB miss cost
 - numa/core's failure to handle 4K pages properly

And addressed those, in the hope of one of them making a
difference.

There's a fourth line of inquiry I'm pursuing as well: the node 
assymetry that David and Paul mentioned could have a performance 
effect as well - resulting from non-ideal placement under 
numa/core.

That is not easy to cure - I have written a patch to take the 
node assymetry into consideration, I'm still testing it with 
David's topology simulated on a testbox:

   numa=fake=4:10,20,20,30,20,10,20,20,20,20,10,20,30,20,20,10

Will send the patch out later.

Thanks,

	Ingo
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