linux-ext4 - Re: [Jfs-discussion] benchmark results

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Date:	Tue, 5 Jan 2010 11:41:17 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Chris Mason <chris.mason@...cle.com>, tytso@....edu,
	Evgeniy Polyakov <zbr@...emap.net>,
	Peter Grandi <pg_jf2@....for.sabi.co.UK>, xfs@....sgi.com,
	reiserfs-devel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-btrfs@...r.kernel.org, jfs-discussion@...ts.sourceforge.net,
	ext-users <ext3-users@...hat.com>, linux-nilfs@...r.kernel.org
Subject: Re: [Jfs-discussion] benchmark results

On Mon, Jan 04, 2010 at 11:27:48AM -0500, Chris Mason wrote:
> On Fri, Dec 25, 2009 at 11:11:46AM -0500, tytso@....edu wrote:
> > On Fri, Dec 25, 2009 at 02:46:31AM +0300, Evgeniy Polyakov wrote:
> > > > [1] http://samba.org/ftp/tridge/dbench/README
> > > 
> > > Was not able to resist to write a small notice, what no matter what, but
> > > whatever benchmark is running, it _does_ show system behaviour in one
> > > or another condition. And when system behaves rather badly, it is quite
> > > a common comment, that benchmark was useless. But it did show that
> > > system has a problem, even if rarely triggered one :)
> > 
> > If people are using benchmarks to improve file system, and a benchmark
> > shows a problem, then trying to remedy the performance issue is a good
> > thing to do, of course.  Sometimes, though the case which is
> > demonstrated by a poor benchmark is an extremely rare corner case that
> > doesn't accurately reflect common real-life workloads --- and if
> > addressing it results in a tradeoff which degrades much more common
> > real-life situations, then that would be a bad thing.
> > 
> > In situations where benchmarks are used competitively, it's rare that
> > it's actually a *problem*.  Instead it's much more common that a
> > developer is trying to prove that their file system is *better* to
> > gullible users who think that a single one-dimentional number is
> > enough for them to chose file system X over file system Y.
> 
> [ Look at all this email from my vacation...sorry for the delay ]
> 
> It's important that people take benchmarks from filesystem developers
> with a big grain of salt, which is one reason the boxacle.net results
> are so nice.  Steve more than willing to take patches and experiment to
> improve a given FS results, but his business is a fair representation of
> performance and it shows.

Just looking at the results there, I notice that the RAID system XFS
mailserver results dropped by an order of magnitude between
2.6.29-rc2 and 2.6.31. The single disk results are pretty
much identical across the two kernels.

IIRC, in 2.6.31 RAID0 started passing barriers through so I suspect
this is the issue. However, seeing as dmesg is not collected by
the scripts after the run and the output of the mounttab does
not show default options, I cannot tell if this is the case. This
might be worth checking by running XFS with the "nobarrier" mount
option....

FWIW, is it possible to get these benchmarks run on each filesystem for
each kernel release so ext/xfs/btrfs all get some regular basic
performance regression test coverage?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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