kern/46325: wapbl + disk io = temporary system freeze

[Christoph_Egger%gmx.de@localhost]

>Number:         46325
>Category:       kern
>Synopsis:       wapbl + disk io = temporary system freeze
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Apr 12 09:40:00 +0000 2012
>Originator:     Christoph Egger
>Release:        netbsd-6 and -current
>Organization:
>Environment:
netbsd/amd64
>Description:

Use NetBSD/amd64 as a desktop system with firefox, thunderbird, openoffice, etc.
Use wapbl.

On heavy disk io the ioflush kernel thread eats up to 60% cpu load
and is in the syncer state. During that time all interrupts are blocked:

- The mouse doesn't move and then jumps.
- Keyboard seems to not work and then suddenly all keys typed appear
  at once.

Here are two outputs of 'top -u' with threads shown during
heavy disk io:

load averages:  0.95,  0.37,  0.16;               up 1+22:59:30                 
  11:31:05
151 threads: 18 idle, 127 sleeping, 2 zombie, 4 on CPU
CPU0 states:  0.0% user,  0.0% nice,  0.0% system, 92.0% interrupt,  8.0% idle
CPU1 states:  0.0% user,  0.0% nice,  4.8% system,  0.0% interrupt, 95.2% idle
CPU2 states:  0.0% user,  0.0% nice,  2.0% system,  0.0% interrupt, 98.0% idle
CPU3 states:  1.2% user,  0.0% nice, 81.2% system,  0.0% interrupt, 17.6% idle
Memory: 3784M Act, 38M Inact, 20K Wired, 188M Exec, 2743M File, 3219M Free
Swap: 8171M Total, 8171M Free

  PID   LID     UID  PRI STATE      TIME   WCPU    CPU NAME      COMMAND
21107     1       0   39 CPU/3      0:54 67.56% 65.53% -         cvs
    0    59       0  124 syncer/3 158:48 48.34% 48.34% ioflush   [system]
    0     4       0  221 IDLE/0     9:03 33.35% 33.35% softbio/0 [system]
[...]


load averages:  1.06,  0.55,  0.24;               up 1+23:00:46                 
  11:32:21
151 threads: 17 idle, 128 sleeping, 1 zombie, 5 on CPU
CPU0 states:  0.0% user,  0.0% nice,  0.0% system,  100% interrupt,  0.0% idle
CPU1 states:  0.0% user,  0.0% nice, 92.0% system,  0.0% interrupt,  8.0% idle
CPU2 states:  0.0% user,  0.0% nice,  1.2% system,  0.0% interrupt, 98.8% idle
CPU3 states:  0.2% user,  0.0% nice,  0.6% system,  0.0% interrupt, 99.2% idle
Memory: 3819M Act, 38M Inact, 20K Wired, 188M Exec, 2770M File, 3184M Free
Swap: 8171M Total, 8171M Free

  PID   LID     UID  PRI STATE      TIME   WCPU    CPU NAME      COMMAND
    0    59       0  124 CPU/1    159:27 61.57% 61.57% ioflush   [system]
21107     1       0  112 tstile/0   1:22 28.54% 28.52% -         cvs
[...]

>How-To-Repeat:

Use wapbl on a desktop system and create heavy disk io.
I create the disk io by updating the pkgsrc tree from cvs.

>Fix: