c4d9468ea0
Avoid using parenthesis enclosure macros (.Pq and .Po/.Pc) with plain text. Not only this slows down the mdoc(7) processing significantly, but it also has an undesired (in this case) effect of disabling hyphenation within the entire enclosed block.
142 lines
4.7 KiB
Groff
142 lines
4.7 KiB
Groff
.\" $NetBSD: ctxsw.9,v 1.2 1996/12/02 00:11:31 tls Exp $
|
|
.\"
|
|
.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to The NetBSD Foundation
|
|
.\" by Paul Kranenburg.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the NetBSD
|
|
.\" Foundation, Inc. and its contributors.
|
|
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
|
|
.\" contributors may be used to endorse or promote products derived
|
|
.\" from this software without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
|
|
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
|
|
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
|
|
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE
|
|
.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
|
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
|
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
|
|
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
|
|
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
|
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
|
|
.\" POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd November 24, 1996
|
|
.Dt MI_SWITCH 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm mi_switch ,
|
|
.Nm cpu_switch ,
|
|
.Nm cpu_throw
|
|
.Nd switch to another process context
|
|
.Sh SYNOPSIS
|
|
.Fd #include <sys/param.h>
|
|
.Fd #include <sys/proc.h>
|
|
.Ft void
|
|
.Fn mi_switch "void"
|
|
.Ft void
|
|
.Fn cpu_switch "void"
|
|
.Ft void
|
|
.Fn cpu_throw "void"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn mi_switch
|
|
function implements the machine independent prelude to a process context
|
|
switch.
|
|
It is called from only a few distinguished places in the kernel
|
|
code as a result of the principle of non-preemtable kernel mode execution.
|
|
The three major uses of
|
|
.Nm
|
|
can be enumerated as follows:
|
|
.Bl -enum -offset indent
|
|
.It
|
|
from within
|
|
.Xr sleep 9
|
|
and
|
|
.Xr tsleep 9
|
|
when the current process
|
|
voluntarily relinquishes the CPU to wait for some resource to become
|
|
available.
|
|
.It
|
|
after handling a trap
|
|
(e.g. a system call, device interrupt)
|
|
when the kernel prepares a return to user-mode execution.
|
|
This case is
|
|
typically handled by machine dependent trap-handling code after detection
|
|
of a change in the signal disposition of the current process, or when a
|
|
higher priority process might be available to run.
|
|
The latter event is
|
|
communicated by the machine independent scheduling routines by calling
|
|
the machine defined
|
|
.Fn need_resched .
|
|
.It
|
|
in the signal handling code
|
|
(see
|
|
.Xr issignal 9 )
|
|
if a signal is delivered that causes a process to stop.
|
|
.El
|
|
.Pp
|
|
.Fn mi_switch
|
|
records the amount of time the current process has been running in the
|
|
process structure and checks this value against the CPU time limits
|
|
allocated to the process
|
|
(see
|
|
.Xr getrlimit 2 ) .
|
|
Exceeding the soft limit results in a
|
|
.Dv SIGXCPU
|
|
signal to be posted to the process, while exceeding the hard limit will
|
|
cause a
|
|
.Dv SIGKILL .
|
|
After these administrative tasks are done,
|
|
.Fn mi_switch
|
|
hands over control to the machine dependent routine
|
|
.Fn cpu_switch ,
|
|
which will perform the actual process context switch.
|
|
.Pp
|
|
.Fn cpu_switch
|
|
first saves the context of the current process.
|
|
Next, it calls
|
|
.Fn chooseproc
|
|
to determine which process to run next.
|
|
Finally, it reads in the saved context of the new process and starts to
|
|
execute the new process.
|
|
.Pp
|
|
.Fn cpu_throw
|
|
is similar to
|
|
.Fn cpu_switch
|
|
except that it does not save the context of the old process.
|
|
This function is useful when the kernel does not have an old process
|
|
context to save, such as when CPUs other than the boot CPU perform their
|
|
first task switch, or when the kernel does not care about the state of the
|
|
old process, such as in
|
|
.Fn cpu_exit
|
|
when the kernel terminates the current process and switches into a new
|
|
process.
|
|
.Pp
|
|
To protect the
|
|
.Xr runqueue 9 ,
|
|
all of these functions must be called with the
|
|
.Va sched_lock
|
|
mutex held.
|
|
.Sh SEE ALSO
|
|
.Xr issignal 9 ,
|
|
.Xr mutex 9 ,
|
|
.Xr runqueue 9 ,
|
|
.Xr tsleep 9 ,
|
|
.Xr wakeup 9
|