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Diffstat (limited to 'static/openbsd/man9/mi_switch.9')
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diff --git a/static/openbsd/man9/mi_switch.9 b/static/openbsd/man9/mi_switch.9 new file mode 100644 index 00000000..b8ecea18 --- /dev/null +++ b/static/openbsd/man9/mi_switch.9 @@ -0,0 +1,111 @@ +.\" $OpenBSD: mi_switch.9,v 1.7 2017/09/05 03:49:56 jmatthew Exp $ +.\" $NetBSD: ctxsw.9,v 1.9 1999/03/06 22:09:29 mycroft 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. +.\" +.\" 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 FOUNDATION 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. +.\" +.Dd $Mdocdate: September 5 2017 $ +.Dt MI_SWITCH 9 +.Os +.Sh NAME +.Nm mi_switch , +.Nm cpu_switchto +.Nd switch to another process context +.Sh SYNOPSIS +.In sys/param.h +.In sys/proc.h +.Ft void +.Fn mi_switch "void" +.Ft void +.Fn cpu_switchto "struct proc *old" "struct proc *new" +.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-preemptable kernel mode execution. +The three major uses of +.Fn mi_switch +can be enumerated as follows: +.Bl -enum -offset indent +.It +From within functions like +.Xr tsleep 9 , +when the current process sleeps to wait for some resource to become +available, or from within functions like +.Fn yield , +when it relinquishes the CPU to allow other processes to make progress. +.It +After handling a trap +.Pq e.g., a system call or 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-dependent +.Fn need_resched "void" . +.It +In the signal handling code +.Pq see Pa sys/kern/kern_sig.c +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 +.Pq 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 +chooses the next process to run and hands over control to the machine +dependent routine +.Fn cpu_switchto , +which will perform the actual process context switch. +.Pp +.Fn cpu_switchto +will save the context of the old process and switch to the new one. +A special case is when the old process is +.Dv NULL +which means that the old process has exited and doesn't need to be +saved. +.Pp +Note that +.Fn mi_switch +and thus +.Fn cpu_switchto +must be called while holding the scheduler lock. +.Sh SEE ALSO +.Xr spl 9 , +.Xr tsleep 9 , +.Xr wakeup 9 |