ia64/183154: kernel{thread taskq} uses 100% CPU

[Anton Shterenlikht]

Number: 183154
Category: ia64
Synopsis: kernel{thread taskq} uses 100% CPU
Confidential: no
Severity: serious
Priority: medium
Responsible: freebsd-ia64
State: open
Class: sw-bug
Submitter-Id: current-users
Arrival-Date: Mon Oct 21 11:40:01 UTC 2013
Originator: Anton Shterenlikht
Release: FreeBSD 11.0-CURRENT ia64

University of Bristol
This host is extremely sluggish.
Periodically all activity seems to freeze
for 5-10-30 sec. For example, issuing ls, df, top
can lead to 10-20 sec. delay before the output
appears.

I noticed that the taskq thread is extremely busy,
sometimes at 100%:

last pid: 50628; load averages: 1.01, 1.09, 1.31 up 0+02:11:37 12:34:43
90 processes: 4 running, 69 sleeping, 15 waiting, 2 lock
CPU 0: 0.0% user, 0.0% nice, 31.6% system, 0.0% interrupt, 68.4% idle
CPU 1: 0.0% user, 0.0% nice, 68.8% system, 0.0% interrupt, 31.3% idle
Mem: 22M Active, 1072M Inact, 411M Wired, 1014M Buf, 8560M Free
Swap:

PID USERNAME PRI NICE SIZE RES STATE C TIME CPU COMMAND
0 root 8 0 0K 416K CPU1 1 97:21 100.00% kernel{thread taskq}
11 root 155 ki31 0K 64K RUN 0 75:53 79.69% idle{idle: cpu0}
11 root 155 ki31 0K 64K RUN 1 71:38 18.90% idle{idle: cpu1}
21 root 16 - 0K 32K *buffe 0 0:41 0.10% syncer
21873 root 20 0 14232K 5800K CPU0 0 0:09 0.10% top
0 root -16 0 0K 416K swapin 0 1:34 0.00% kernel{swapper}
13 root -8 - 0K 96K - 0 0:18 0.00% geom{g_down}

This is probably just a symptom of a deeper problem.