150 lines
4.0 KiB
Groff
150 lines
4.0 KiB
Groff
.\" $NetBSD: cpu_switchto.9,v 1.14 2011/06/03 08:06:54 wiz Exp $
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.\"
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.\" Copyright (c)2007 YAMAMOTO Takashi,
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" ------------------------------------------------------------
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.Dd June 2, 2011
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.Dt CPU_SWITCHTO 9
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.Os
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.\" ------------------------------------------------------------
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.Sh NAME
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.Nm cpu_switchto
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.Nd machine-dependent
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.Tn LWP
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context switching interface
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.\" ------------------------------------------------------------
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.Sh SYNOPSIS
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.In sys/cpu.h
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.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.Ft lwp_t *
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.Fn cpu_switchto \
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"lwp_t *oldlwp" "lwp_t *newlwp" "bool returning"
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.\" ------------------------------------------------------------
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.Sh DESCRIPTION
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The
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.Fn cpu_switchto
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function saves the context of the
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.Tn LWP
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which is currently running on the processor,
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and restores the context of the
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.Tn LWP
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specified by
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.Fa newlwp .
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.Pp
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Remarks:
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.Bl -enum -offset indent
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.It
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.Fn cpu_switchto
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does not switch address spaces.
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.It
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.Fn cpu_switchto
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sets
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.Xr curlwp 9
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to
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.Fa newlwp .
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If the architecture does non-interlocked adaptive mutex release,
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.Fn cpu_switchto
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does an equivalent of
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.Xr membar_producer 3 ,
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before and after the modification of
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.Xr curlwp 9 .
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.It
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.Fn cpu_switchto
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should be called at
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.Dv IPL_SCHED .
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When the function returns, the caller should lower
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the priority level as soon as possible.
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.It
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.Fn cpu_switchto
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might be called with spin mutexes held.
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.El
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.Pp
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The function takes the following arguments.
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.Bl -tag -width "returning " -offset indent
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.It Fa oldlwp
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Specify the
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.Tn LWP
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from which the switch is going to be made, i.e., the calling
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.Tn LWP .
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If it was
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.Dv NULL ,
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the context of the
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.Tn LWP
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currently running on this processor is not saved.
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.It Fa newlwp
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Specify the
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.Tn LWP
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to which to switch.
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It must not be
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.Dv NULL .
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.It Fa returning
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Only meaningful if the architecture implements fast software interrupts.
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If true, it indicates that
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.Fa oldlwp
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is a soft interrupt
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.Tn LWP
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that is blocking.
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It is a good indication that any kind of address space or user activity
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can be completely ignored.
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For example:
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.Xr ras_lookup 9 ,
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cache flushes, TLB wirings, adjusting lazy
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.Tn FPU
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state.
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All that is required is to restore the register state and stack, and
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return to the interrupted
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.Tn LWP .
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.El
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.\" ------------------------------------------------------------
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.Sh RETURN VALUES
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The
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.Fn cpu_switchto
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function does not return until another
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.Tn LWP
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calls
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.Fn cpu_switchto .
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It returns the
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.Vt oldlwp
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argument of the
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.Fn cpu_switchto
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which is called to switch back to our
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.Tn LWP .
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It is either a
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.Tn LWP
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which called
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.Fn cpu_switchto
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to switch to us or
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.Dv NULL
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in case the
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.Tn LWP
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was exiting.
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.\" ------------------------------------------------------------
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.Sh SEE ALSO
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.Xr membar_producer 3 ,
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.Xr swapcontext 3 ,
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.Xr intro 9 ,
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.Xr mutex 9 ,
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.Xr spl 9
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