linux-kernel - Re: [PATCH 16/35] writeback: increase min pause time on concurrent dirtiers

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Message-ID: <1292352908.13513.376.camel@laptop>
Date:	Tue, 14 Dec 2010 19:55:08 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Valdis.Kletnieks@...edu
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@....de>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Theodore Ts'o <tytso@....edu>,
	Chris Mason <chris.mason@...cle.com>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Greg Thelen <gthelen@...gle.com>,
	Minchan Kim <minchan.kim@...il.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 16/35] writeback: increase min pause time on concurrent
 dirtiers

On Tue, 2010-12-14 at 13:42 -0500, Valdis.Kletnieks@...edu wrote:
> On Tue, 14 Dec 2010 14:51:33 +0800, Wu Fengguang said:
> 
> > > > +	/* (N * 10ms) on 2^N concurrent tasks */
> > > > +	t = (hi - lo) * (10 * HZ) / 1024;
> > > 
> > > Either I need more caffeine, or the comment doesn't match the code
> > > if HZ != 1000?
> > 
> > The "ms" in the comment may be confusing, but the pause time (t) is
> > measured in jiffies :)  Hope the below patch helps.
> 
> 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=100 kernel?

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