Re: elevator algorithm considered irrelevant

Mark Lord (mlord@pobox.com)
Tue, 17 Nov 1998 13:38:31 +0000

Larry McVoy wrote:
> I wanted to mention that back around 1990 or so I spent a bunch of
> time trying improve performance by playing with the disk sort routine
> (the elevator alg) in SunOS. I futzed around for several weeks before
> realizing that it didn't much matter what I did. That was the insight.

Base assumptions may have changed somewhat since then..
Drive speeds are now faster, partitions are much larger,
Linux is not SunOS (async vs. sync I/O), ext2fs is not ufs.

I once implemented "closest seek" and "2way-elevators" for
the Linux IDE driver, and saw marked response improvements
under heavy load. In practice, starvation of the edges was
a non-issue, though I'm sure a pathological case could be
conceived that might be noticeably malaffected.

"closest seek" was the better performing of the methods tried.

The code was simple, and based on a 1.0 kernel, and no longer
fits, and I don't even have it anymore. Feel free to reimplement.

Of course, base assumptions may have changed somewhat since then..

Cheers

-- 
mlord@pobox.com
former IDE guy


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