linux-ext4 - Re: ext4 write performance regression in 3.6-rc1

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Date:	Fri, 17 Aug 2012 09:40:39 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Marti Raudsepp <marti@...fo.org>,
	Kernel hackers <linux-kernel@...r.kernel.org>,
	ext4 hackers <linux-ext4@...r.kernel.org>, maze@...gle.com,
	"Shi, Alex" <alex.shi@...el.com>, linux-fsdevel@...r.kernel.org
Subject: Re: ext4 write performance regression in 3.6-rc1

On Fri, Aug 17, 2012 at 02:09:15PM +0800, Fengguang Wu wrote:
> Ted,
> 
> I find ext4 write performance dropped by 3.3% on average in the
> 3.6-rc1 merge window. xfs and btrfs are fine.
> 
> Two machines are tested. The performance regression happens in the
> lkp-nex04 machine, which is equipped with 12 SSD drives. lkp-st02 does
> not see regression, which is equipped with HDD drives. I'll continue
> to repeat the tests and report variations.

Hmm... I've checked out the commits in "git log v3.5..v3.6-rc1 --
fs/ext4 fs/jbd2" and I don't see anything that I would expect would
cause that.  The are the lock elimination changes for Direct I/O
overwrites, but that shouldn't matter for your tests which are
measuring buffered writes, correct?

Is there any chance you could do me a favor and do a git bisect
restricted to commits involving fs/ext4 and fs/jbd2?

Many thanks,

						- Ted
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