ioflush kernel thread chewing CPU time

[Simon Burge <simonb%NetBSD.org@localhost>]

Hi folks,

Has anyone seen a problem where the ioflush kernel thread uses a lot of
CPU time?

I've recently upgraded my dual CPU i386 laptop from a September 2008
-current kernel to a netbsd-5 kernel from March 12.  I am using WAPBL on
the four ffs filesystems.  After a couple of days, I noticed the system
was really sluggish and found the ioflush kernel thread was using a
lot of CPU time.  I've rebooted, and then another fews days later same
issue.

The top three CPU time users from "top -t" right now are:

  PID   LID USERNAME PRI STATE      TIME   WCPU    CPU COMMAND      NAME
    0    49 root     124 syncer/0  18.7H 23.34% 23.34% [system]     ioflush
    0    12 root      96 smtask/0   9:25  0.00%  0.00% [system]     sysmon
    0     9 root     125 cacheg/0   0:11  0.00%  0.00% [system]     cachegc

Before I start digging, anyone else seen anything like this before?  I
notice a few commits from Andy Doran around late February in the syncer,
but it's not obvious if any of these fix the problems at a quick glance.

Cheers,
Simon.