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Date: Sun, 16 Sep 2007 22:19:08 +0200 (MEST)
From: Michiel Boland <michiel@boland.org>
To: freebsd-current@freebsd.org
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Subject: PREEMPTION on UP systems
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-CURRENT UP systems with

options PREEMPTION

exhibit some very 'jerky' and annoying behaviour. In particular, if you 
have, say, a buildkernel running somewhere, interactive behaviour in all 
alther applications goes down the toilet. You can very easily reproduce 
this by opening some file and vi and just moving the cursor back and forth 
(press and hold 'l' and 'h'). You will see the cursors miss beats and 
genereally just behave very jumpy. It appears to be disk-io related.

Sorry I can't be more specific. It's just that someone else also mentioned 
something about strange perormance issues on UP boxen. So my suggestion 
would be to take out the PREEMPTION option and see how that goes. 
(Obviously, you can't have SCHED_ULE then also.)

Cheers
Michiel