104 lines
3.3 KiB
Groff
104 lines
3.3 KiB
Groff
.\" $NetBSD: sched_4bsd.9,v 1.3 2008/04/30 13:10:58 martin Exp $
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.\"
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.\" Copyright (c) 2002 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Gregory McGarry and Daniel Sieger.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd July 14, 2007
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.Dt SCHED_4BSD 9
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.Os
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.Sh NAME
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.Nm sched_4bsd
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.Nd The 4.4BSD thread scheduler
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.Sh SYNOPSIS
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.In sys/sched.h
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.Ft void
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.Fn resetpriority "lwp_t *l"
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.Ft void
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.Fn sched_tick "struct cpu_info *ci"
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.Ft void
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.Fn sched_schedclock "lwp_t *l"
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.Ft void
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.Fn sched_pstats_hook "struct proc *p" "int minslp"
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.Ft void
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.Fn sched_setrunnable "lwp_t *l"
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.Ft void
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.Fn updatepri "lwp_t *l"
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.Sh DESCRIPTION
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The
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.Nx
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thread scheduling sub-system employs a
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.Dq multilevel feedback queues
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algorithm, favouring interactive, short-running threads to
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CPU-bound ones.
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.Pp
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.Fn resetpriority
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recomputes the priority of a thread running in user mode.
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If the resulting priority is higher than that of the
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current thread, a reschedule is arranged.
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.Pp
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.Fn sched_tick
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gets called from
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.Xr hardclock 9
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every 100ms to force a switch between equal priority threads.
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.Pp
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The priority of the current thread is adjusted through
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.Fn sched_schedclock .
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The priority of a thread gets worse as it accumulates CPU time.
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.Pp
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.Fn sched_pstats_hook
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gets called from
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.Fn sched_pstats
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every Hz ticks in order to recompute the priorities of all threads.
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.Pp
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.Fn sched_setrunnable
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checks if an LWP has slept for more than one second.
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If so, its priority is updated by
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.Fn updatepri .
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.Sh CODE REFERENCES
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This section describes places within the
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.Nx
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source tree where actual code implementing the scheduler can be found.
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All pathnames are relative to
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.Pa /usr/src .
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.Pp
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The 4.4BSD scheduler subsystem is implemented within the file
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.Pa sys/kern/sched_4bsd.c .
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.Sh SEE ALSO
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.Xr csf 9 ,
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.Xr hardclock 9 ,
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.Xr mi_switch 9 ,
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.Xr userret 9
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.Rs
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.%A Marshall Kirk McKusick
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.%A Keith Bostic
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.%A Michael J. Karels
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.%A John S. Quarterman
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.%B "The Design and Implementation of the 4.4BSD Operating System"
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.%I "Addison Wesley"
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.%D 1996
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.Re
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