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Date: Mon, 29 May 2006 16:35:22 -0700
From: Nate Lawson <nate@root.org>
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Subject: Intermittent hangs appeared in recent -current?
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During disk I/O, I now get hangs about every 30 seconds.  Running sync 
manually doesn't seem to cause this.  I also get minor pauses 
periodically.  Just after the system is hung, top shows that 80% of the 
time is spent in system.

Overall, it seems like a lot of time is being spent in g_up/g_down but I 
think that's normal.
USER    PID %CPU %MEM   VSZ   RSS  TT  STAT STARTED      TIME COMMAND
root     10 41.4  0.0     0     8  ??  RL    3:37PM   2:04.01 [idle]
root      3 23.2  0.0     0     8  ??  DL    3:37PM   3:55.80 [g_up]
root      4 15.8  0.0     0     8  ??  DL    3:37PM   2:41.11 [g_down]
nate   1022 11.1  0.4  8864  3060  p1  RL+   4:05PM   1:03.11 cvs up
root     37  1.2  0.0     0     8  ??  DL    3:37PM   0:12.87 [syncer]

Example just after hang:
2.3% user,  0.0% nice, 82.6% system,  0.8% interrupt, 14.3% idle

Example during cvs up but no hang:
1.6% user,  0.0% nice, 52.7% system,  0.8% interrupt, 45.0% idle

I noticed the clock interrupt and/or psm (irq 12) waiting on *Giant near 
when the hang occurs so perhaps someone is holding Giant too long.

I'm just running a nearly stock GENERIC with ata:
FreeBSD 7.0-CURRENT #4: Sun May  7 14:12:55 PDT 2006

-- 
Nate