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

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Date:	Tue, 16 Mar 2010 20:18:09 -0700 (PDT)
From:	Ben Gamari <bgamari.foss@...il.com>
To:	tytso@....edu
Cc:	linux-kernel@...r.kernel.org, Olly Betts <olly@...vex.com>,
	martin f krafft <madduck@...duck.net>
Subject: Re: Poor interactive performance with I/O loads with fsync()ing

Sorry about the lack of any useful information in my initial email.
I clearly didn't read it before sending.

On Tue, 16 Mar 2010 21:24:39 -0400, tytso@....edu wrote:
> What kernel version are you using; what distribution and what version
> of that distro are you running; what file system are you using and
> what if any mount options are you using?  And what kind of hard drives
> do you have?

While this problem has been around for some time, my current configuration
is the following:

  Kernel 2.6.32 (although also reproducible with kernels at least as early as 2.6.28)
  Filesystem: Now Btrfs (was ext4 less than a week ago), default mount options
  Hard drive: Seagate Momentus 7200.4 (ST9500420AS)
  Distribution: Ubuntu 9.10 (Karmic)

> 
> I'm going to assume you're running into the standard ext3
> "data=ordered" entagled writes problem.  There are solutions, such as
> switching to using ext4, mounting with data=writeback mode, but they
> have various shortcomings.
> 
Unfortunately several people have continued to encounter unacceptable
latency, even with ext4 and data=writeback.

> A number of improvements have been made in ext3 and ext4 since some of
> the discussions you quoted, but since you didn't tell us what
> distribution version and/or what kernel version you are using, we
> can't tell you are using those newer improvements yet.
>
Sorry about that. I should know better by now.

- Ben
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