Re: [ANNOUNCE] RSDL completely fair starvation free interactive cpu scheduler

On Tuesday 06 March 2007 05:29, Simon Arlott wrote:
On 04/03/07 22:27, Con Kolivas wrote:
On Monday 05 March 2007 09:19, Simon Arlott wrote:
If I run glxgears, thunderbird/firefox become really slow to
respond/display and cpu usage isn't even at 100%. I had thunderbird
lagging on keyboard character repeat earlier but can't reproduce that
now even with glxgears - however firefox lags really badly on keyboard
input with glxgears running.

Hi Simon

You're hitting a nasty udev bug here that is unrelated to the cpu
scheduler

Yes, I've already reported this.

and almost certainly responsible for your bad behaviour.

What? How do you make the leap from lockdep output on boot to my experience
of slow interactive response?

In general I've found once the kernel did something funny on boot that not
much beyond that could be trusted. However a very small period of alarm with
lockdep, _assuming it was transient and did not happen later_ as you say,
would not cause problems.

Also this patch was actually for 2.6.20 and you seem to have applied it
to 2.6.21-rc2. I haven't even checked that it cleanly applies to that
kernel.

It doesn't, a one line fix from Ingo conflicts (and a comment that was
changed). 7355690ead6d61f6344072ae61060f985060da29 [PATCH] sched: fix SMT
scheduler bug 72fd4a35a824331d7a0f4168d7576502d95d34b3 [PATCH] Numerous
fixes to kernel-doc info in source files.

Ok, but I was very reluctant to release this code as a patch to -rc2 because
the potential for all sorts of weird and wonderful fireworks and explosions
from the -pre release makes it a lousy testing ground for something else.
It's often hard to differentiate breakage in behaviour in the unstable kernel
or the patch you're applying. I was even somewhat reluctant to be releasing
this patch for 2.6.20 since people are mumbling (offlist) that they're
getting weird stalls on that kernel - however they're afraid to report them
to lkml since their issues are fuzzy and they know they'll be ask to do git
bisect on an intermittent problem; git bisect as we know is rocket science
(or brain surgery if you happen to be a rocket scientist).

I have reverted your patch and the laggy behaviour remains when running
glxgears (in fact it seems a bit worse), I don't know about the thunderbird
lag while typing since I can't easily reproduce it but I don't recall it
ever happening before. So, your patch isn't the cause of a serious slowdown
when running glxgears in the background (although it doesn't improve the
situation much). It looks like it just slows down X in general rather than
using much CPU.

Which goes back to my original comment about glxgears, only I should have made
my advice stronger; glxgears should not be used as a benchmarking or test
tool of any sort period. It displays pretty gears and that's all. On your
machine, for example, it is not cpu bound from the looks of your description,
and either loads up the bus or drowns the gpu in ways that delays other gpu
activity. On other hardware combinations, it does something completely
different. Given that, it's easy to see how it is impossible to use it as a
cpu scheduling test of any sort.

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