kern/38792: sched_pstats takes too long

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>Number:         38792
>Category:       kern
>Synopsis:       sched_pstats takes too long
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu May 29 23:40:00 +0000 2008
>Originator:     Andrew Doran
>Release:        4.99.63
>Organization:
The NetBSD Project
>Environment:
n/a/
>Description:
sched_pstats() can take a long time if there are thousands of procs/LWPs
in the system.

That's a problem because it runs in interrupt context, and because 
realtime threads might need access to the process list.
 
>How-To-Repeat:
Testing.
>Fix:
Maybe:

- Make sched_pstats use a marker process so it does not hold proc_lock
  for so long?

- Have two classes of callout, like Solaris. One run from a softint
  as we do now, and another run from a kthread, for slow items like
  sched_pstats.