linux-ext4 - Re: Excessive stall times on ext4 in 3.9-rc2

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Message-ID: <20130403152249.GB4908@suse.de>
Date:	Wed, 3 Apr 2013 16:22:50 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: Excessive stall times on ext4 in 3.9-rc2

On Tue, Apr 02, 2013 at 07:16:13PM -0400, Theodore Ts'o wrote:
> I've tried doing some quick timing, and if it is a performance
> regression, it's not a recent one --- or I haven't been able to
> reproduce what Mel is seeing.  I tried the following commands while
> booted into 3.2, 3.8, and 3.9-rc3 kernels:
> 
> time git clone ...
> rm .git/index ; time git reset
> 

FWIW, I had run a number if git checkout based tests over time and none
of them revealed anything useful. Granted it was on other machines but I
don't think it's git on its own. It's a combination that leads to this
problem. Maybe it's really an IO scheduler problem and I need to figure
out what combination triggers it.

> <SNIP>
>
> Mel, how bad is various git commands that you are trying?  Have you
> tried using time to get estimates of how long a git clone or other git
> operation is taking?
> 

Unfortunately, the milage varies considerably and it's not always
possible to time the operation. It may be that one occasion that opening
a mail takes an abnormal length time with git operations occasionally
making it far worse.

-- 
Mel Gorman
SUSE Labs
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