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

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Message-ID: <20130402231613.GA4946@thunk.org>
Date:	Tue, 2 Apr 2013 19:16:13 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Mel Gorman <mgorman@...e.de>
Cc:	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

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

I did this a number of git repo's; including one that was freshly
cloned, and one that had around 3 dozen patches applied via git am (so
there were a bunch of loose objects).  And I tried doing this on an
SSD and a 5400rpm HDD, and I did it with all of the in-memory cache
flushed via "git 3 > /proc/sys/vm/drop_caches".  The worst case was
doing a "time git reset" after deleting the .git/index file after
applying all of Kent Overstreet's recent AIO patches that had been
sent out for review.  It took around 55 seconds, on 3.2, 3.8 and
3.9-rc3.  That is pretty horrible, but for me that's the reason why I
use SSD's.

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?

						- Ted
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