linux-kernel - Re: [PATCH 3/3] mm: page allocator: Drain per-cpu lists after direct reclaim allocation fails

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Message-ID: <20100904075840.GE705@dastard>
Date:	Sat, 4 Sep 2010 17:58:40 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Mel Gorman <mel@....ul.ie>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 3/3] mm: page allocator: Drain per-cpu lists after
 direct reclaim allocation fails

On Fri, Sep 03, 2010 at 08:21:01PM -0700, Andrew Morton wrote:
> On Sat, 4 Sep 2010 12:25:45 +1000 Dave Chinner <david@...morbit.com> wrote:
> 
> > Still, given the improvements in performance from this patchset,
> > I'd say inclusion is a no-braniner....
> 
> OK, thanks.
> 
> It'd be interesting to check the IPI frequency with and without -
> /proc/interrupts "CAL" field.  Presumably it went down a lot.

Maybe I suspected you would ask for this. I happened to dump
/proc/interrupts after the livelock run finished, so you're in
luck :)

The lines below are:

before: before running the single 50M inode create workload
after: the numbers after the run completes
livelock: the numbers after two runs with a livelock in the second

Vanilla 2.6.36-rc3:

before:      561   350   614   282   559   335   365   363
after:	   10472 10473 10544 10681  9818 10837 10187  9923

.36-rc3 With patchset:

before:      452   426   441   337   748   321   498   357
after:      9463  9112  8671  8830  9391  8684  9768  8971

The numbers aren't that different - roughly 10% lower on average
with the patchset. I will state that vanilla kernel runs I ijust did
had noticably more consistent performance than the previous results
I had acheived, so perhaps it wasn't triggering the livelock
conditions as effectively this time through.

And finally:

livelock:  59458 58367 58559 59493 59614 57970 59060 58207

So the livelock case tends to indicate roughly 40,000 more IPI
interrupts per CPU occurred.  The livelock occurred for close to 5
minutes, so that's roughly 130 IPIs per second per CPU....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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