Oddities in -current post-eventtimer

Matthew D. Fuller fullermd at over-yonder.net
Mon Jan 3 10:46:33 UTC 2011

OK, this has happened a couple times now.  I'm running a mid-Oct
-CURRENT, and at around 25 days uptime (not exact but consistently in
that vicinity), things start getting very choppy.  It's easily visible
in playing videos; things get very jerky and slow, but all sorts of
things start acting like they're happening in little chunks of time;
keyboard repeats get very slow, things that often take notable time
take much more, etc.  It's accompanied by a big spat of "calcru:
runtime went backwards" messages (presumably just another symptom).

The only fix I've found is to reboot, and then it's good for another
25ish days.  As a workaround, enabling kern.eventtimer.idletick sets
things rightish.  A look at the interrupts turns up a hint; while
vmstat says the overall average for cpu0 is just under 300/s, systat
-vmstat shows that it's currnetly running around 20-some.  The other
CPU's also settle at much lower levels.

Another more tiring workaround is just slinging the mouse around real
fast; that seems to hint to the system to keep checking stuff.
Watching systat, that doesn't seem to bring the cpuX interrupt rate up
very much, but the videos start playing smoothly.

FreeBSD 9.0-CURRENT #0 r214107: Wed Oct 20 06:25:50 CDT 2010
Quad-core running amd64.

Matthew Fuller     (MF4839)   |  fullermd at over-yonder.net
Systems/Network Administrator |  http://www.over-yonder.net/~fullermd/
           On the Internet, nobody can hear you scream.

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