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SubjectFwd: Adaptive read-ahead V12
----- Forwarded message from Iozone <capps@iozone.org> -----

Subject: Adaptive read-ahead V12
From: Iozone <capps@iozone.org>
To: Wu Fengguang <wfg@mail.ustc.edu.cn>
X-Mailer: Microsoft Outlook Express 6.00.2900.2670
Date: Thu, 25 May 2006 11:44:37 -0500

Wu Fengguang,

I see that Andrew M. is giving you some pushback....
His argument is that the application could do a better job
of scheduling its own read-ahead. ( I've heard this one
before)

My thoughts on this argument would be along the
lines of:

Indeed the application might be able to do a better
job, however expecting, or demanding, the rewrite
of all applications to behave better might be an unreasonable
expectation. Rewriting all the weather codes, all the
structrual analysis codes, all the data-bases, video streaming
and so on, would solve the problem but the timeline for
such an re-codification may approach infinity, while
systems that have the ability to silently increase
performance maintain an advantage in the market.
Note: Many vendors already have sophisticated A.I. read-ahead
algorithms. Examples: Microsoft, Veritas HP, and Isolon.

Linux already does read-ahead that does not require
the application to be involved. It just does it in
a simpler way that could be improved for handling
a wider range of applications. This new technology is
a simple evolutionary step in that direction. Linux read-ahead
and is currently 8 years behind existing technologies in this area.
Isn't it time to catch up a bit ?

Note: You probably will need to reword this before replying
to Andrew, as I tend to be somewhat blunt. :-)

Hint: I took me a while to convince the kernel folks in my
company to accept such a technology. But when the
prototype accelerated one of their key partner's code by
30 % wall clock, and another showed 50X speedup in
file I/O across a wide stripe, that did the trick.

Enjoy,
Don Capps

[...]
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