Re: elevator algorithm bug in ll_rw_blk.c

H. Peter Anvin (hpa@transmeta.com)
16 Nov 1998 03:58:56 GMT

Followup to: <Pine.LNX.3.96.981115160941.3229F-100000@52-a-usw.rb1.blv.nwnexus.net>
By author: Tim Smith <tzs@tzs.net>
In newsgroup: linux.dev.kernel
>
> On Sun, 15 Nov 1998, Vojtech Pavlik wrote:
> > You could apply a two way elevator well if you knew about the physical
> > characteristics of the drive. Unfortunately there is no way to find that out
> > for most modern drives.
>
> Actually, by analyzing timings on carefully selected request sequences, you
> can figure out pretty much all of the physical characteristics of most
> drives. See
>
> http://www.ece.cmu.edu/~ganger/papers/
>

Do you really want to bother keeping track of them, especially since
modern drives have different numbers of sectors per track?

I think the current algorithm (a) works well, (b) avoids penalizing
part of the disk, and (c) is simple.

-hpa

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