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SubjectRe: New Benchmark tools, lookie looky........
On Tue, Oct 17, 2000 at 11:23:30AM +0200, Vojtech Pavlik wrote:
> Well, I know quite well what this can bring us - with precise profiling
> we could see the exact geometry of the drive

LMbench has had something which does this for years. Look at

http://www.bitmover.com/bw.gif
http://www.bitmover.com/seek.gif

The first shows you zone bandwidths, the second shows you a precise profile
of the access times; you can get everything you might want from that.
For example, the time quoted by all the drive people is 1/3 in from the
left, at the bottom of the curve - a fairly misleading number if you ask
me.

The benchmark is in disk.c.

> However I don't believe this can bring us significant performance
> enhancements and it will make the elevator algorithm even more complex
> than it is now. For the OS it's more important the fairness of disk i/o
> scheduling for example is much much more important than the perfect
> ordering (in relation to what the drive would like to see) of the
> accesses.

Bingo. Screwing around with the elevator is in general a waste of time,
but it is a rite of passage for all I/O people. I did it a long time
ago and learned an important lesson: if your file system is good enough
(and most are) there is almost nothing that can be done to improve
performance - the file system has done all the work already. You're
welcome to argue that point, but please do so with traces of a real
system - not with your opinion. My opinion used to be the opposite
and the traces moved me to this opinion.
--
---
Larry McVoy lm at bitmover.com http://www.bitmover.com/lm
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