First ext3 data (was Re: 2.5 readpages doubles cifs vfs large file copy performance vs. 2.4)

[David Collier-Brown -- Customer Engineering]

David Collier-Brown -- Customer Engineering wrote:
 >  The data I have from qfs and ufs on Solaris says bigger is better
 > until you get too big, but it's fairly insensitive once you get
 > past too small.  The usual u-shaped curve, with a very wide
 > "sweet spot".
 >
 >  If the sweet spot on Linux is large, it's going to be easy. If
 > it's hard to hit, then I have to start looking carefully at the
 > criteria.

I just did the initial test of increasing the filesystem
read size on ext3 on an IDE disk, and there is indeed
a moderate payoff in throughput for the case where
the read size is  significant chunk of the file size,
as you'd expect.

What is interesting, however, is the shape of the
absolute time curve. It has a very wide "sweet spot",
starts to fall off at high buffer sizes, but that's
where the small payoff really has value (in throughput),
so it's credible to say that Linux EXT3 on a single
IDE drive has a wide "sweet spot".

Gifs attached: the different lines are for different
file sizes, the other data is labeled. (hey, it's
a spreadsheet graph, not an analysis (;-))

--dave
-- 
David Collier-Brown,           | Always do right. This will gratify
Sun Microsystems DCMO          | some people and astonish the rest.
Toronto, Ontario               |
(905) 415-2849 or x52849       | davecb at canada.sun.com

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