7.0-PRERELEASE desktop system periodically freezes momentarily

J.R. Oldroyd fbsd at opal.com
Wed Jan 23 10:57:13 PST 2008

On Wed, 23 Jan 2008 08:27:58 -0700, Joe Peterson <joe at skyrush.com> wrote:
> Also, it seems that intermittent mouse freezes happen more often when
> I've been away from the machine for a while and return to start using
> the mouse again, but that's not always the case.  A few short
> freezes/stutters happen a second or so after mouse movement resumes.
> 					-Joe


I don't see any postings from you showing any ktr dumps.  Do you have
any?  Your symptoms (that it seems to happen after you've been away
for a while and then return and move the mouse) sound a lot like mine.

I posted some ktr dumps and have since chatted off-list with Kris and
Sam about what may be up.  My dumps show the shared irq ath/pcm and
the ath taskq are hogging the cpu for ages without the clock swi getting
to run at all.  Sam has suggested experimenting with the ath taskq
priority and also with disabling ath bg scans which I will do, but
right now I am back to looking at powerd again as the possible cause.

I ran without powerd for a while when originally suggested by David
Lawrence on Jan 12th.  I believe I did still see freezes then, but I
re-enabled powerd when I was ready to do LOCK_PROFILING and then ktr
monitoring; I re-enabled it so I could be sure I had the same test
conditions.  At this point, I am no longer sure what happened when
powerd was disabled.  My recollection is that there were freezes while
powerd was off, but the only email in which I appear to have posted
about that says "no freezes so far".  So I'm running without powerd again,
and at this point, several hours at the computer over two days, I have
not seen further freezes.  Does anyone else who sees these freezes also
have powerd enabled and can try without powerd for a while?

Since these freezes are proving so hard to pinpoint, it may be worth
comparing notes to try to find things in common between the systems
or eliminate other things.  But first, it seems like we may be chasing
three separate causes:

    1. the softupdate freeze
	after removing a very large file (e.g., >1Gb) there is a
	noticeable freeze while the softupdate runs 

    2. the busy freeze
	folk complain of short freezes and mouse jerkiness while
	the system is busy, e.g., glxgears or compilations

    3. the idle freeze
	short and longer freezes (some going into minutes) apparently
	when resuming work after having left the system mostly idle
	for a while

Now, I also had the "busy freeze" when I first tested 7.0.  At that time
(several weeks back now) someone suggested switching to the ULE scheduler,
which I did, and the symptoms I had were dramatically improved.  Since
then I've had occasions to run several compilations at once and had no
mouse jerkiness.  But for folk who still have it: what scheduler do you
have and what processes are running when it happens?

At the moment, I'm chasing an "idle freeze".  In other emails, I've
posted details of what processes are typically running and several ktr
dumps of such events.  As noted, I'm looking again into powerd right
now, and if that isn't it, I'll go to the ath taskq prio and scan stuff
that Sam suggested.  Anyone else with an idle freeze care to post
details of what scheduler and processes are in use?

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