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

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Message-ID: <1292358255.13513.390.camel@laptop>
Date:	Tue, 14 Dec 2010 21:24:15 +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 15:13 -0500, Valdis.Kletnieks@...edu wrote:
> So you're not guaranteed that 10*HZ is 10 seconds.  10*USER_HZ, sure.
> But not HZ.

You're confused. 10*HZ jiffies is always 10 seconds. Hertz means
per-second. We take CONFIG_HZ ticks per second, so waiting HZ jiffies
makes us wait 1 second.

USER_HZ is archaic and only used to stabilize user-interfaces that for
some daft reason depended on HZ.
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