Messages in this thread | | | Date | Tue, 17 Oct 2000 08:12:40 -0700 | From | Larry McVoy <> | Subject | Re: New Benchmark tools, lookie looky........ |
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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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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