linux-kernel - Re: [PATCH 2/5] writeback: dirty position control

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Date:	Fri, 26 Aug 2011 21:13:41 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	Greg Thelen <gthelen@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrea Righi <arighi@...eler.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] writeback: dirty position control

On Fri, Aug 26, 2011 at 08:20:57PM +0800, Wu Fengguang wrote:
> On Fri, Aug 26, 2011 at 08:11:50PM +0800, Peter Zijlstra wrote:
> > On Fri, 2011-08-26 at 19:26 +0800, Wu Fengguang wrote:
> > > Now I get 3 figures. Test case is: run 1 dd write task for 300s, with
> > > a "disturber" dd read task during roughly 120-130s. 
> > 
> > Ah, but ideally the disturber task should run in bursts of 100ms
> > (<feedback period), otherwise your N is indeed mostly constant.
> 
> Ah yeah, the disturber task should be a dd writer! Then we get
> 
> - 120s: N=1 => N=2
> - 130s: N=2 => N=1

Here they are. The write disturber starts/stops around 150s.

We got similar result as in the read disturber case, even though one
disturbs N and the other impacts writeout bandwith.  The original
patchset is consistently performing much better :)

Thanks,
Fengguang

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