120 lines
4.1 KiB
Groff
120 lines
4.1 KiB
Groff
.\" $NetBSD: setrunqueue.9,v 1.8 2005/12/20 19:53:15 rpaulo Exp $
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.\"
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.\" Copyright (c) 2001, 2002 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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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 December 20, 2005
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.Dt SETRUNQUEUE 9
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.Os
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.Sh NAME
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.Nm setrunqueue ,
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.Nm remrunqueue ,
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.Nm nextrunqueue
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.Nd manipulate system run queue
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.Sh SYNOPSIS
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.In sys/proc.h
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.In sys/sched.h
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.Ft void
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.Fn setrunqueue "struct lwp *l"
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.Ft void
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.Fn remrunqueue "struct lwp *l"
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.Ft struct lwp *
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.Fn nextrunqueue "void"
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.Sh DESCRIPTION
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The
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.Fn setrunqueue ,
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.Fn remrunqueue ,
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and
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.Fn nextrunqueue
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functions manipulate the system queue of runnable processes.
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The system scheduler uses this queue to find the highest-priority process
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when a process switch occurs.
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These functions are generally machine-dependent implementations in order
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to permit efficient implementation of priority-based process selection.
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.Pp
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.Bf -symbolic
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Currently, these functions are scheduler specific and correspond to
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the default
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.Dq time-sharing
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scheduler in
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.Nx .
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Their implementation is likely to change in the future to cater for
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different schedulers.
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.Ef
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.Pp
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The priority queue consists of an array
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.Va sched_qs[NQS]
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of queue header structures each of which identifies a list of runnable
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processes of equal priority.
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Lower indices in
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.Va sched_qs
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indicate higher priority.
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A single word
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.Va sched_whichqs
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containing a bit mask identifying non-empty queues assists in
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selecting a process quickly.
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The running process is on no queue, other processes are on a queue related
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to p->p_priority, divided by 4 actually to shrink the 0-127 range of
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priorities into the 32 available queues.
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.Pp
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The
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.Fn setrunqueue
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function places the given process on the system run queue.
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It is an error to call
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.Fn setrunqueue
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with a process that is not runnable or that is already on the system
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run queue or sleep queue.
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.Pp
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The
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.Fn remrunqueue
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function removes the given process from the system run queue.
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It is an error to call
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.Fn remrunqueue
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with a process that is not on the system run queue.
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.Pp
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The
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.Fn nextrunqueue
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function will make a choice amongst the processes which are ready to
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run from the priority run queue.
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.Fn nextrunqueue
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will remove the first process from the list on the queue with the
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highest priority a return it.
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.Pp
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These functions must be called with the scheduler lock held
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.Pq see Xr SCHED_LOCK 9
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and at the
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.Xr splsched 9
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interrupt protection level,
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.Sh SEE ALSO
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.Xr SCHED_LOCK 9 ,
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.Xr scheduler 9 ,
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.Xr splsched 9
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