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

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Date:	Wed, 21 Nov 2012 11:14:50 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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

On Mon, Nov 19, 2012 at 11:37:01PM -0800, David Rientjes wrote:
> On Tue, 20 Nov 2012, Ingo Molnar wrote:
> 
> > No doubt numa/core should not regress with THP off or on and 
> > I'll fix that.
> > 
> > As a background, here's how SPECjbb gets slower on mainline 
> > (v3.7-rc6) if you boot Mel's kernel config and turn THP forcibly
> > off:
> > 
> >   (avg: 502395 ops/sec)
> >   (avg: 505902 ops/sec)
> >   (avg: 509271 ops/sec)
> > 
> >   # echo never > /sys/kernel/mm/transparent_hugepage/enabled
> > 
> >   (avg: 376989 ops/sec)
> >   (avg: 379463 ops/sec)
> >   (avg: 378131 ops/sec)
> > 
> > A ~30% slowdown.
> > 
> > [ How do I know? I asked for Mel's kernel config days ago and
> >   actually booted Mel's very config in the past few days, 
> >   spending hours on testing it on 4 separate NUMA systems, 
> >   trying to find Mel's regression. In the past Mel was a 
> >   reliable tester so I blindly trusted his results. Was that 
> >   some weird sort of denial on my part? :-) ]
> > 
> 
> I confirm that numa/core regresses significantly more without thp than the 
> 6.3% regression I reported with thp in terms of throughput on the same 
> system.  numa/core at 01aa90068b12 ("sched: Use the best-buddy 'ideal cpu' 
> in balancing decisions") had 99389.49 SPECjbb2005 bops whereas 
> ec05a2311c35 ("Merge branch 'sched/urgent' into sched/core") had 122246.90 
> SPECjbb2005 bops, a 23.0% regression.
> 

I also see different regressions and gains depending on the number of
warehouses. For low number of warehouses without THP the regression was
severe but flat for higher number of warehouses. I explained in another
mail that specjbb reports based on peak figures and regressions outside
the peak can be missed as a result so we should watch out for that.

-- 
Mel Gorman
SUSE Labs
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