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Changes since 1.2: +1 -8 lines

Convert TNF licenses to new 2 clause variant

.\"     $NetBSD: sched_4bsd.9,v 1.3 2008/04/30 13:10:58 martin 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 and Daniel Sieger.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\"
.Dd July 14, 2007
.Dt SCHED_4BSD 9
.Os
.Sh NAME
.Nm sched_4bsd
.Nd The 4.4BSD thread scheduler
.Sh SYNOPSIS
.In sys/sched.h
.Ft void
.Fn resetpriority "lwp_t *l"
.Ft void
.Fn sched_tick "struct cpu_info *ci"
.Ft void
.Fn sched_schedclock "lwp_t *l"
.Ft void
.Fn sched_pstats_hook "struct proc *p" "int minslp"
.Ft void
.Fn sched_setrunnable "lwp_t *l"
.Ft void
.Fn updatepri "lwp_t *l"
.Sh DESCRIPTION
The
.Nx
thread scheduling sub-system employs a
.Dq multilevel feedback queues
algorithm, favouring interactive, short-running threads to
CPU-bound ones.
.Pp
.Fn resetpriority
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
.Fn sched_tick
gets called from
.Xr hardclock 9
every 100ms to force a switch between equal priority threads.
.Pp
The priority of the current thread is adjusted through
.Fn sched_schedclock .
The priority of a thread gets worse as it accumulates CPU time.
.Pp
.Fn sched_pstats_hook
gets called from
.Fn sched_pstats
every Hz ticks in order to recompute the priorities of all threads.
.Pp
.Fn sched_setrunnable
checks if an LWP has slept for more than one second.
If so, its priority is updated by
.Fn updatepri .
.Sh CODE REFERENCES
This section describes places within the
.Nx
source tree where actual code implementing the scheduler can be found.
All pathnames are relative to
.Pa /usr/src .
.Pp
The 4.4BSD scheduler subsystem is implemented within the file
.Pa sys/kern/sched_4bsd.c .
.Sh SEE ALSO
.Xr csf 9 ,
.Xr hardclock 9 ,
.Xr mi_switch 9 ,
.Xr userret 9
.Rs
.%A Marshall Kirk McKusick
.%A Keith Bostic
.%A Michael J. Karels
.%A John S. Quarterman
.%B "The Design and Implementation of the 4.4BSD Operating System"
.%I "Addison Wesley"
.%D 1996
.Re