linux-kernel - Re: [patch] 2.6.21-rc4 nicksched v32

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Date:	Fri, 23 Mar 2007 13:33:41 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Al Boldi <a1426z@...ab.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [patch] 2.6.21-rc4 nicksched v32

Al Boldi wrote:
> Nick Piggin wrote:

>>Timeslices get scaled by /proc/sys/kernel/base_timeslice. If you have bad
>>interactivity you could try lowering this and see if it helps.
> 
> 
> As I am on 2.6.20, I can't really test this patch, but I tried your sched 
> from PlugSched and its not bad.

OK, the one in plugsched is reasonably different...

> I'm getting strange numbers with chew.c, though.  Try this:
> Boot into /bin/sh
> Run ./chew on one console.
> Run ./chew on another console.
> Watch latencies.
> 
> Console 1:
> pid 671, prio   0, out for  799 ms, ran for  800 ms, load  50%
> pid 671, prio   0, out for  799 ms, ran for  801 ms, load  50%
> pid 671, prio   0, out for  799 ms, ran for  799 ms, load  49%
> pid 671, prio   0, out for  800 ms, ran for  800 ms, load  49%
> 
> Console 2:
> pid 672, prio   0, out for  800 ms, ran for  799 ms, load  49%
> pid 672, prio   0, out for  799 ms, ran for  800 ms, load  50%
> pid 672, prio   0, out for  799 ms, ran for  800 ms, load  50%
> pid 672, prio   0, out for  799 ms, ran for  799 ms, load  49%
> pid 672, prio   0, out for  799 ms, ran for  799 ms, load  49%
> 
> Looks good, but now add a cpu-hog, ie. while :; do :; done
> 
> Console 1:
> 
> pid 671, prio   0, out for  799 ms, ran for  399 ms, load  33%
> pid 671, prio   0, out for  799 ms, ran for  399 ms, load  33%
> pid 671, prio   0, out for  799 ms, ran for  399 ms, load  33%
> pid 671, prio   0, out for  799 ms, ran for  399 ms, load  33%
> 
> Console 2:
> pid 672, prio   0, out for 1599 ms, ran for  799 ms, load  33%
> pid 672, prio   0, out for 1599 ms, ran for  799 ms, load  33%
> pid 672, prio   0, out for 1599 ms, ran for  800 ms, load  33%
> pid 672, prio   0, out for 1599 ms, ran for  799 ms, load  33%
> 
> It's smooth, but latencies are double on console2.  Easy enough to fix, 
> though, just press scrollock to induce a sleep and then release.

Yeah, this issue is since fixed in v32.

> Also, latencies are huge.  Is there a way to fix latencies per nice?

Latencies should be quite a bit lower in v32. You can lower it
with /proc/sys/kernel/base_timeslice, however I would like to see
whether the current setting gives reasonable interactivity.

Thanks,
Nick

-- 
SUSE Labs, Novell Inc.
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