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Subject: Re: [PATCH 16/35] writeback: increase min pause time on concurrent
 dirtiers
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
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Date: Tue, 14 Dec 2010 19:55:08 +0100
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To: Valdis.Kletnieks@vt.edu
Cc: Wu Fengguang <fengguang.wu@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>, Dave Chinner <david@fromorbit.com>, Christoph Hellwig <hch@lst.de>, Trond Myklebust <Trond.Myklebust@netapp.com>, Theodore Ts'o <tytso@mit.edu>, Chris Mason <chris.mason@oracle.com>, Mel Gorman <mel@csn.ul.ie>, Rik van Riel <riel@redhat.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Greg Thelen <gthelen@google.com>, Minchan Kim <minchan.kim@gmail.com>, linux-mm <linux-mm@kvack.org>, "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
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On Tue, 2010-12-14 at 13:42 -0500, Valdis.Kletnieks@vt.edu wrote:
> On Tue, 14 Dec 2010 14:51:33 +0800, Wu Fengguang said:
>=20
> > > > +	/* (N * 10ms) on 2^N concurrent tasks */
> > > > +	t =3D (hi - lo) * (10 * HZ) / 1024;
> > >=20
> > > Either I need more caffeine, or the comment doesn't match the code
> > > if HZ !=3D 1000?
> >=20
> > The "ms" in the comment may be confusing, but the pause time (t) is
> > measured in jiffies :)  Hope the below patch helps.
>=20
> No, I meant that 10 * HZ evaluates to different numbers depending what
> the CONFIG_HZ parameter is set to - 100, 250, 1000, or some other
> custom value.  Does this code behave correctly on a CONFIG_HZ=3D100 kerne=
l?

10*HZ =3D 10 seconds
(10*HZ) / 1024 ~=3D 10 milliseconds

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