Re: disk head scheduling
Mark H. Wood (mwood@iupui.edu)
Fri, 19 Mar 1999 07:04:45 -0500 (EST)
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.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/