kern/45053: priority queue support for workqueue(9)

[Jukka Ruohonen <jruohonen%iki.fi@localhost>]

>Number:         45053
>Category:       kern
>Synopsis:       priority queue support for workqueue(9)
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    kern-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sun Jun 12 06:15:00 +0000 2011
>Originator:     Jukka Ruohonen
>Release:        5.99.52
>Organization:
-
>Environment:

>Description:

There has been some discussions about deprecating sysmon_taskq(9) on the
basis that only one interface, i.e. workqueue(9) in this case, should be
used, and that sysmon_taskq(9) may contain possible locking issues.

However, for this to be possible, workqueue(9) must support priorities.
In other words, it must be possible to schedule high/medium/low/etc. tasks
such that the oldest task of the highest priority is always run first.

(This requirement comes from acpi(4) where the "notifications" from the SCI
interrupt must always run before the notifications to the listeners/drivers.)

>How-To-Repeat:

Code inspection.

>Fix:

Implement priorities for workqueue(9).