Messages in this thread | | | Date | Fri, 19 Mar 1999 07:04:45 -0500 (EST) | From | "Mark H. Wood" <> | Subject | Re: disk head scheduling |
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On Fri, 19 Mar 1999, Ingo Molnar wrote: > On Thu, 18 Mar 1999, Yasushi Saito wrote: > > What I tried to implement was two-way elevator seeking (SCAN). In my > > tiny benchmark that let many threads write on random files, SCAN > > showed a throughput improvement of anywhere between 0 to 20%. But I > > also noticed benefits in the original algorithm (it's fairer), so I > > don't know if my change makes sense. > > the bigger problem is that dumber devices will just execute non-forwards > ordered requests. Most modern harddisks will either cache a full track, or > will reorder the request per-track anyway, but eg. a floppy disk or a > CD-ROM will execute the requests as given, and the 'downwards' queue will > perform badly. Would you mind doing the seek benchmark on your CDROM too, > just to test this theory?
Well of course a 2-way elevator should sort by *ascending* sector within descending track. I take it this is difficult?
-- Mark H. Wood, Lead System Programmer mwood@IUPUI.Edu Specializing in unusual perspectives for more than twenty years.
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