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Diffstat (limited to 'share/man/man9/mi_switch.9')
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diff --git a/share/man/man9/mi_switch.9 b/share/man/man9/mi_switch.9 new file mode 100644 index 000000000000..fe97bc5ed921 --- /dev/null +++ b/share/man/man9/mi_switch.9 @@ -0,0 +1,165 @@ +.\" $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 thread context +.Sh SYNOPSIS +.In sys/param.h +.In 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 thread context +switch. +It is called from only a few distinguished places in the kernel +code as a result of the principle of non-preemptable kernel mode execution. +The various major uses of +.Nm +can be enumerated as follows: +.Bl -enum -offset indent +.It +From within a function such as +.Xr cv_wait 9 , +.Xr mtx_lock , +or +.Xr tsleep 9 +when the current thread +voluntarily relinquishes the CPU to wait for some resource or lock 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 thread 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. +.It +When a thread dies in +.Xr thread_exit 9 +and control of the processor can be passed to the next runnable thread. +.It +In +.Xr thread_suspend_check 9 +where a thread needs to stop execution due to the suspension state of +the process as a whole. +.El +.Pp +.Fn mi_switch +records the amount of time the current thread has been running in the +process structures 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 . +.Pp +If the thread is still in the +.Dv TDS_RUNNING +state, +.Fn mi_switch +will put it back onto the run queue, assuming that +it will want to run again soon. +If it is in one of the other +states and KSE threading is enabled, the associated +.Em KSE +will be made available to any higher priority threads from the same +group, to allow them to be scheduled next. +.Pp +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 thread context switch. +.Pp +.Fn cpu_switch +first saves the context of the current thread. +Next, it calls +.Fn choosethread +to determine which thread to run next. +Finally, it reads in the saved context of the new thread and starts to +execute the new thread. +.Pp +.Fn cpu_throw +is similar to +.Fn cpu_switch +except that it does not save the context of the old thread. +This function is useful when the kernel does not have an old thread +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 thread, such as in +.Fn thread_exit +when the kernel terminates the current thread and switches into a new +thread. +.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 cv_wait 9 , +.Xr issignal 9 , +.Xr mutex 9 , +.Xr runqueue 9 , +.Xr tsleep 9 , +.Xr wakeup 9 |