97 lines
3.4 KiB
Groff
97 lines
3.4 KiB
Groff
.\" $NetBSD: cpu_idle.9,v 1.3 2003/04/16 13:35:26 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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.\" 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 September 21, 2002
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.Dt CPU_IDLE 9
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.Os
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.Sh NAME
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.Nm cpu_idle
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.Nd idle CPU while waiting for work
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.Sh SYNOPSIS
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.In sys/proc.h
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.Ft void
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.Fn cpu_idle "void"
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.Sh DESCRIPTION
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The
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.Fn cpu_idle
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function is invoked to idle the current CPU while waiting for work to be done.
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It is primarily called by the scheduler if no processes are
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available on the system run queue.
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The
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.Fn cpu_idle
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function is a machine-dependent implementations in order to permit
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low-level CPU control.
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.Pp
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The
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.Fn cpu_idle
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function must be called with the scheduler lock held
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.P 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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It performs the following operations:
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.Bl -bullet
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.It
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Release the scheduler lock.
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.It
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Lower the current interrupt priority level to permit interrupts to be
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taken that will eventually cause processes to appear again on the
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system run queue.
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.It
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Try to zero some pages for the virtual memory system.
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.It
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Perform any CPU or system power control.
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.It
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Wait until a process appears on the system run queue.
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.It
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Acquire the scheduler lock.
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.El
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.Pp
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For CPUs which don't support an idle operation, the CPU must spin
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until a process appears on the system run queue.
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Generally, this is done by checking if the
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.Va sched_whichqs
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variable in the scheduler is not zero.
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See
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.Xr setrunqueue 9
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for further details.
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.Sh SEE ALSO
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.Xr mi_switch 9 ,
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.Xr scheduler 9 ,
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.Xr setrunqueue 9 ,
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.Xr spl 9 ,
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.Xr uvm 9
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