linux-ext4 - Re: new ext4 filesystem vs. converted ext3

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Date:	Mon, 06 Jun 2011 12:43:10 -0400
From:	micah anderson <micah@...eup.net>
To:	Ted Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: new ext4 filesystem vs. converted ext3

On Fri, 3 Jun 2011 23:09:49 -0400, Ted Ts'o <tytso@....edu> wrote:
> On Fri, Jun 03, 2011 at 05:49:17PM -0400, Micah Anderson wrote:
> > However, ever since I did that change, I've noticed an increase in I/O
> > wait state on the CPUs. I've been trying to determine why, and if there
> > were some things I should tune on this ext4 filesystem.
> 
> How are you measuring this?

Through munin graphs, unfortunately we don't have a lot of data from
before the change, but you can see the jump early on in this graph,
where the change was made:

http://lackof.org/~taggart/tmp/willet-cpu-year.png

I'll note that we also moved to squeeze from lenny at this
time. Basically we decided to move to squeeze and then convert to ext4,
so that throws in some other variables here too.

As I mentioned before, this is a high traffic mailing list system, which
does a lot of I/O. We're also seeing lots of rescheduling interrupts
after the upgrade to the squeeze kernel:

http://lackof.org/~taggart/tmp/willet-irqstats-year.png

(see the jump in the pink line on the left side?)

Searches on "rescheduling interrupts" finds lots of people using
powertop to try to reduce their laptop power usage (this might be
related: https://help.ubuntu.com/community/ReschedulingInterrupts), I'm
wondering if maybe there were changes from lenny to squeeze to try and
optimize for that, but are hurting in our case.

micah

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