Re: [RFC] - Some notions that I would like comments on

Chuck Lever (cel@monkey.org)
Tue, 13 Jul 1999 13:32:27 -0400 (EDT)

On Mon, 12 Jul 1999 cd_smith@ou.edu wrote:
> With the caveat that I didn't write the original message (so I may be the
> one without a clue here) I think a few people are missing the point on
> this speculative I/O thing. I don't know that it's a good idea, but it's
> at least worth understanding and evaluating. As I see it, the big
> difference between "speculative" I/O and asynchronous I/O is the
> interface. Speculative I/O would appear to be a blocking I/O call, but as
> soon as it queued the I/O request, it would return. The result page would
> be marked as unreadable and unwriteable, and the actual I/O blocking would
> be done on a page fault.

there's a good paper related to this published in the OSDI '99
proceedings. see:

Chang, F., Gibson, G., "Automatic I/O Hint Generation through Speculative
Execution," Proceedings of the Third Symposium on Operating Systems Design
and Implementation, pp. 1-14, February 1999.

the authors used speculative execution during I/O waits to predict future
read requests instead of the method you described. their conclusion was
that were good gains from speculative execution, but the technique
requires significant O/S complexity.

- Chuck Lever

--
corporate:	<chuckl@netscape.com>
personal:	<chucklever@netscape.net> or <cel@monkey.org>


The Linux Scalability project:
	http://www.citi.umich.edu/projects/linux-scalability/




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