Re: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]

From: Kurt Garloff (garloff@suse.de)
Date: Mon Feb 10 2003 - 15:33:53 EST

On Mon, Feb 10, 2003 at 10:02:48AM +0100, Andrea Arcangeli wrote:
> On Mon, Feb 10, 2003 at 07:27:51PM +1100, Nick Piggin wrote:
> It doesn't make any sense to me your claim that you can decrease the
> readahead by adding anticipatory scheduling, if you do you'll run
> so slow at 8k per request in all common workloads.

Readahead kills seeks and command overhead at the expense of maybe
transfering data needlessly over the bus and consuming RAM.

AS kills seeks. (At the expense of delaying some IO a tiny bit.)

If unecessary seeks are the main problem, with AS smaller READA is
possible. If command overhead is a problem, READA needs to be large.

Regards, 

-- 
Kurt Garloff  <garloff@suse.de>                          Eindhoven, NL
GPG key: See mail header, key servers                 SuSE Labs (Head)
SuSE Linux AG, Nuernberg, DE                            SCSI, Security
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