Xorg 6.8.1 and SCHED_ULE vs. SCHED_4BSD

Kevin Oberman oberman at es.net
Tue Mar 1 00:21:40 GMT 2005

> Date: Sun, 27 Feb 2005 21:36:23 +0100
> From: Godwin Stewart <gstewart at bonivet.net>
> Sender: owner-freebsd-stable at freebsd.org
> Hash: SHA1
> On Sat, 26 Feb 2005 21:49:00 +0100, Michael Nottebrock
> <michaelnottebrock at gmx.net> wrote:
> > I've been using that for a long time now, since Xorg 6.8.1 breaks vt-
> > switching for me.
> Well, I decided to bite the bullet and upgraded to Xorg 6.8.1 anyway. It
> didn't break vt-switching for me, thankfully. Other than the core keyboard
> driver being "kbd" instead of "Keyboard" now, which threw me off for a
> couple of minutes, all went well. It seems to be stable enough. Cross
> fingers, touch wood etc.
> I also took advantage of the latest cvsup to 5.4-PRE and ensuing recompile
> to revert to SCHED_4BSD from SCHED_ULE and PREEMPTION in the kernel. The
> difference is staggering.
> One of the things I've been doing is to record some of my old cassettes
> (you know, those old plastic things with 2 holes and a tape inside :) onto
> CD. Applying a FFT filter to 50 minutes of audio takes between 10 and 15
> minutes on this machine (P-III/550, 384MB) depending on the complexity of
> the filter. During this time, with SCHED_ULE and PREEMTION, the machine is
> unusable. It freezes hard for periods of 10-12 seconds and then when it
> unfreezes (while doing disk i/o apparently) the keys you typed turn up in
> the wrong order.
> However, now that I've reverted to SCHED_4BSD, the machine remains
> perfectly snappy while performing the FFT filter, which doesn't happen
> perceptibly slower.
> It could be that I misread things entirely (wouldn't be the first time),
> but wasn't SCHED_ULE's purpose to *improve* the responsiveness of the
> machine when under load? The results I'm getting here are, errmm...
> slightly different... Old hardware maybe?

This is VERY odd. What you saw with ULE is what I (and most people) saw
with 4BSD. I got very tired of the short pauses I was getting unde 4BSD
on my 5-Stable laptop and was very pleased to get back to ULE a few weeks
ago when I moved it to 6-Current.

I'd say something is very wrong on your systems and I'd ALMOST bet it's
ata related. Maybe ATA-MkIII would help things out.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634

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