1.\" $NetBSD: cpu_need_resched.9,v 1.9 2011/10/24 07:30:29 yamt Exp $ 2.\" 3.\" Copyright (c) 2002 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Gregory McGarry. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd July 31, 2010 31.Dt CPU_NEED_RESCHED 9 32.Os 33.Sh NAME 34.Nm cpu_need_resched 35.Nd context switch notification 36.Sh SYNOPSIS 37.In sys/cpu.h 38.Ft void 39.Fn cpu_need_resched "struct cpu_info *ci" "int flags" 40.Sh DESCRIPTION 41The 42.Fn cpu_need_resched 43function is the machine-independent interface for the scheduler to 44notify machine-dependent code that a context switch from the current 45LWP, on the cpu 46.Fa ci , 47is required. 48This event may occur if a higher priority LWP appears on the run 49queue or if the current LWP has exceeded its time slice. 50.Pp 51If 52.Dv RESCHED_KPREEMPT 53flag is specified in 54.Fa flags 55and 56.Dv __HAVE_PREEMPTION 57C pre-processor macro is defined in 58.In machine/intr.h , 59machine-dependent code should make a context switch happen as soon as possible 60even if the cpu is running the kernel code. 61.Pp 62If 63.Dv RESCHED_IMMED 64flag is specified in 65.Fa flags , 66machine-dependent code should make a context switch happen as soon as possible. 67In that case, for example, if 68.Fa ci 69is not the current processor, 70.Fn cpu_need_resched 71typically issues an inter processor call to the processor to make it 72notice the need of a context switch as soon as possible. 73.Pp 74Typically, the 75.Fn cpu_need_resched 76function will perform the following operations: 77.Bl -bullet -offset indent 78.It 79Set a per-processor flag which is checked by 80.Xr userret 9 81when returning to user-mode execution. 82.It 83Post an asynchronous software trap 84.Pq Tn AST . 85.It 86Send an inter processor interrupt to wake up 87.Xr cpu_idle 9 . 88.El 89.Sh SEE ALSO 90.Xr sched_4bsd 9 , 91.Xr userret 9 92