Update to describe current API (only), and not duplicate that can be

found elsewhere. (And which will appear in the NetBSD Internals Guide
soonish).

Submitted by Daniel Sieger <dsieger@TechFak.Uni-Bielefeld.DE>,
OK'd by martin@ and  yamt@

share/man/man9/scheduler.9

@@ -1,10 +1,10 @@
-.\"     $NetBSD: scheduler.9,v 1.3 2003/04/16 13:35:33 wiz Exp $
+.\"     $NetBSD: scheduler.9,v 1.4 2006/12/04 15:36:23 hubertf Exp $
 .\"
 .\" Copyright (c) 2002 The NetBSD Foundation, Inc.
 .\" All rights reserved.
 .\"
 .\" This code is derived from software contributed to The NetBSD Foundation
-.\" by Gregory McGarry.
+.\" by Gregory McGarry and Daniel Sieger.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
@@ -34,82 +34,79 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd September 21, 2002
+.Dd December 2, 2006
 .Dt SCHEDULER 9
 .Os
 .Sh NAME
-.Nm scheduler
-.Nd process scheduling subsystem
+.Nm scheduler ,
+.Nm resetpriority ,
+.Nm roundrobin ,
+.Nm rqinit ,
+.Nm schedclock ,
+.Nm schedcpu ,
+.Nm setrunnable ,
+.Nm updatepri
+.Nd thread scheduling sub-system
 .Sh SYNOPSIS
 .In sys/sched.h
+.In sys/lwp.h
+.In sys/proc.h
+.Ft void
+.Fn resetpriority "struct lwp *l"
+.Ft void
+.Fn roundrobin "struct cpu_info *ci"
+.Ft void
+.Fn schedclock "struct lwp *l"
+.Ft void
+.Fn schedcpu "void *arg"
+.Ft void
+.Fn setrunnable "struct lwp *l"
+.Ft void
+.Fn updatepri "struct lwp *l"
 .Sh DESCRIPTION
-.Bf -symbolic
-This page documents the default
-.Dq time-sharing
-scheduler in
-.Nx .
-It is likely that in the future a new scheduler subsystem will be
-developed which will allow new scheduling algorithms to be
-implemented.
-.Ef
 .Pp
-.Nx Ns 's
-scheduler algorithm is based on
-.Dq multilevel feedback queues .
-All processes that are runnable are assigned a scheduling priority
-that determines in which run queue they are placed.
-The currently running process does not exist on a run queue.
-In selecting a new process to run, the system scans the run queues
-from highest to lowest priority and chooses the first process on the
-first non-empty queue.
-If multiple processes reside on a queue, the system runs them round
-robin in the order found on the queue.
-If a process uses up the time slice allocated to it, it is placed at
-the end of the queue from which it came, and the process at the front of
-the queue is selected to run.
+The
+.Nx
+thread scheduling sub-system employs a
+.Dq multilevel feedback queues
+algorithm, favouring interactive, short-runnig threads to 
+CPU-bound ones.
 .Pp
-The system adjusts the scheduling priority of a process dynamically to
-reflect resource requirements (being blocked) and the CPU utilization
-consumed by the process.
-Processes are moved between run queues based on changes in their
-scheduling priority (hence the word feedback in the name).
-.Pp
-The process CPU utilization is incremented in
-.Fn hardclock
-each time that the system clock ticks and the process is found to be
-executing.
-CPU utilization is adjusted once per second in
-.Fn schedcpu
-via a digital decay filter.
-Each time a process accumulates four ticks in its CPU utilization,
-.Fn schedclock
-invokes
 .Fn resetpriority
-to recalculate the process's scheduling priority.
+recomputes the priority of a thread running in
+user mode. If the resulting priority is higher than that of the
+current thread, a reschedule is arranged.
 .Pp
-When a process other than the currently running process attains a
-higher scheduling priority, the system notices this in
-.Fn resetpriority
-and schedules a context switch to the higher-priority process to occur
-on return to user mode.
+.Fn roundrobin
+gets called from
+.Xr hardclock 9
+every 100ms to force a switch between equal priority threads.
 .Pp
-A blocked process exists on the sleep queue and is not affected by the
-scheduling behaviour discussed above.
-However, each second
+The runqueues are initialized through
+.Fn rqinit ,
+called from
+.Fn init_main
+at system startup.
+.Pp
+The priority of the current thread is adjusted through
+.Fn schedclock .
+The priority of a thread gets worse as it accumulates CPU time.
+.Pp
+The
 .Fn schedcpu
-updates the time each process has been on the sleep queue.
-The system recomputes a process's CPU utilization estimate in
+function recomputes the priorities of all threads every Hz
+ticks.
+.Pp
+The
+.Fn setrunnable
+function changes a thread's state to be runnable. If the thread is in
+memory, it is placed on the proper runqueue, according to its
+priority. Otherwise the swapper is awaked.
+.Pp
+The
 .Fn updatepri
-when it is awakened and has been sleeping for longer than 1 second.
-When the process is placed on the run queue by
-.Fn setrunnable ,
-.Fn resetpriority
-is invoked to recalculate the process's scheduling priority.
-.Pp
-The system tailors this short-term scheduling algorithm to favor
-interactive jobs by raising the scheduling priority of processes that
-are blocked waiting for I/O for one or more seconds, and by lowering the
-priority of processes that accumulate significant amounts of CPU time.
+function recalculates the priority of a thread after it has been
+sleeping.
 .Sh CODE REFERENCES
 This section describes places within the
 .Nx