linux-kernel - Re: [PATCH 00/13] IO-less dirty throttling

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Message-ID: <20101119022824.GB13830@dastard>
Date:	Fri, 19 Nov 2010 13:28:24 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Christoph Hellwig <hch@....de>, Theodore Ts'o <tytso@....edu>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/13] IO-less dirty throttling

On Wed, Nov 17, 2010 at 05:59:00PM -0800, Andrew Morton wrote:
> On Thu, 18 Nov 2010 12:40:51 +1100 Dave Chinner <david@...morbit.com> wrote:
> > Yeah, sorry, should have posted them - I didn't because I snapped
> > the numbers before the run had finished. Without series:
> > 
> > 373.19user 14940.49system 41:42.17elapsed 612%CPU (0avgtext+0avgdata 82560maxresident)k
> > 0inputs+0outputs (403major+2599763minor)pagefaults 0swaps
> > 
> > With your series:
> > 
> > 359.64user 5559.32system 40:53.23elapsed 241%CPU (0avgtext+0avgdata 82496maxresident)k
> > 0inputs+0outputs (312major+2598798minor)pagefaults 0swaps
> > 
> > So the wall time with your series is lower, and system CPU time is
> > way down (as I've already noted) for this workload on XFS.
> 
> How much of that benefit is an accounting artifact, moving work away
> from the calling process's CPU and into kernel threads?

As I spelled out in my original results, the sustained CPU usage for
the unmodified kernel is ~780% - 620% fs_mark, 80% bdi-flusher, 80%
kswapd (i.e. completely CPU bound on the 8p test VM).  With this
series, the sustained CPU usage is about 380% - 250% fs_mark, 80%
bdi-flusher, 50% kswapd.

IOWs, this series _halved_ the total sustained CPU usage even after
taking into account all the kernel threads. With wall time also
being reduced and the number of IOs issued dropping by 25%, I find
it hard to classify the result as anything other than spectacular...

Cheers,

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