80 lines
2.8 KiB
Groff
80 lines
2.8 KiB
Groff
.\" $NetBSD: cpu_need_resched.9,v 1.7 2008/05/25 19:45:43 wiz 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.
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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 May 18, 2007
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.Dt CPU_NEED_RESCHED 9
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.Os
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.Sh NAME
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.Nm cpu_need_resched
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.Nd context switch notification
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.Sh SYNOPSIS
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.In sys/cpu.h
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.Ft void
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.Fn cpu_need_resched "struct cpu_info *ci" "int flags"
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.Sh DESCRIPTION
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The
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.Fn cpu_need_resched
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function is the machine-independent interface for the scheduler to
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notify machine-dependent code that a context switch from the current
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LWP, on the cpu
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.Fa ci ,
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is required.
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This event may occur if a higher priority LWP appears on the run
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queue or if the current LWP has exceeded its time slice.
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.Pp
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If
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.Dv RESCHED_IMMED
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flag is specified in
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.Fa flags ,
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machine-dependent code should make a context switch happen as soon as possible.
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In that case, for example, if
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.Fa ci
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is not the current processor,
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.Fn cpu_need_resched
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typically issues an inter processor call to the processor to make it
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notice the need of a context switch as soon as possible.
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.Sh EXAMPLES
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Specifically, the
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.Fn cpu_need_resched
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function will perform the following operations:
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.Bl -bullet -offset indent
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.It
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Set a per-processor flag which is checked by
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.Xr userret 9
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when returning to user-mode execution.
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.It
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Post an asynchronous software trap (AST).
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.It
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Send an inter processor interrupt to wake up
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.Fn cpu_idle .
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.El
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.Sh SEE ALSO
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.Xr sched_4bsd 9 ,
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.Xr userret 9
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