Messages in this thread |  | | Date | Sat, 10 Aug 1996 17:47:29 +0100 (BST) | From | Bryn Paul Arnold Jones <> | Subject | Re: "Elevator ordering" and other oddities |
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On Fri, 9 Aug 1996, Rakesh Dubey wrote:
> > > > Sorry for the interruption, but there's some really excellent > > information coming out of the I/O scheduling discussions. Problem is > > that I don't understand a lot of it. > > > > Can anyone point me to a good "newless cluebie" introduction to, at > > the least, the terminology. I've no formal CS training (high school > > doesn't count), but I'm reasonably familiar with the kernel internals. > > > > Again, thanks. > > I believe that "The Design of BSD 4.3" has some details on elevator > algorithm for ordering disk accesses. > > The real idea is simple and uses the fact that it takes considerably > more time to position the disk head than to actually transfer the > data. So if we can minumize disk head movements we would save > time. Now look at a stream of I/O requests and reorder it so that the > accesses are towards the center of the disk (i.e. decreasing cylinder > number) and then after a point towards the periphery of the disk. In > order, you go up and then down. >
I think you just described saw tooth ...
> -Rakesh > Bryn -- PGP key pass phrase forgotten, \ Overload -- core meltdown sequence again :( and I don't care ;) | initiated. / This space is intentionally left | blank, apart from this text ;-) \____________________________________
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