linux-kernel - Re: Poor interactive performance with I/O loads with fsync()ing

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Date:	Tue, 23 Mar 2010 20:51:46 +0100
From:	Jesper Krogh <jesper@...gh.cc>
To:	Ben Gamari <bgamari.foss@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Poor interactive performance with I/O loads with fsync()ing

Ben Gamari wrote:
> Hey all,
> 
> Recently I started using the Xapian-based notmuch mail client for everyday
> use.  One of the things I was quite surprised by after the switch was the
> incredible hit in interactive performance that is observed during database
> updates. Things are particularly bad during runs of 'notmuch new,' which scans
> the file system looking for new messages and adds them to the database.
> Specifically, the worst of the performance hit appears to occur when the
> database is being updated.

I would suggest that you include a 2.6.31 kernel in your testing. I have
seen something that seems like "huge" stalls in 2.6.32 but I havent been
able to "dig into it" to find more.

In 2.6.32 I have seen IO-wait numbers around 80% on a 16 core machine
with 128GB of memory and load-numbers over 120 under workloads that
didn't make 2.6.31 sweat at all.

Filesystems are a mixture of ext3 and ext4 (so it could be the barriers)?

-- 
Jesper
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