linux-kernel - Re: [RFC PATCH] cfq-iosched: IOPS mode for group scheduling and new group

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Message-ID: <20100728235716.GA12945@infradead.org>
Date:	Wed, 28 Jul 2010 19:57:16 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Heinz Diehl <htd@...cy-poultry.org>, linux-kernel@...r.kernel.org,
	jaxboe@...ionio.com, nauman@...gle.com, dpshah@...gle.com,
	guijianfeng@...fujitsu.com, jmoyer@...hat.com, czoccolo@...il.com
Subject: Re: [RFC PATCH] cfq-iosched: IOPS mode for group scheduling and new
 group_idle tunable

On Wed, Jul 28, 2010 at 04:22:12PM -0400, Vivek Goyal wrote:
> I also did "time firefox &" testing to see how long firefox takes to
> launch when linus torture test is running and without patch it took
> around 20 seconds and with patch it took around 17 seconds. 
> 
> So to me above test results suggest that this patch does not worsen
> the performance. In fact it helps. (at least on ext3 file system.)
> 
> Not sure why are you seeing different results with XFS.

So why didn't you test it with XFS to verify his results?  We all know
that different filesystems have different I/O patters, and we have
a history of really nasty regressions in one filesystem by good meaning
changes to the I/O scheduler.

ext3 in fact is a particularly bad test case as it not only doesn't have
I/O barriers enabled, but also has particularly bad I/O patterns
compared to modern filesystems.

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