1.\" $NetBSD: cpu_switchto.9,v 1.14 2011/06/03 08:06:54 wiz Exp $ 2.\" 3.\" Copyright (c)2007 YAMAMOTO Takashi, 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25.\" SUCH DAMAGE. 26.\" 27.\" ------------------------------------------------------------ 28.Dd June 2, 2011 29.Dt CPU_SWITCHTO 9 30.Os 31.\" ------------------------------------------------------------ 32.Sh NAME 33.Nm cpu_switchto 34.Nd machine-dependent 35.Tn LWP 36context switching interface 37.\" ------------------------------------------------------------ 38.Sh SYNOPSIS 39.In sys/cpu.h 40.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 41.Ft lwp_t * 42.Fn cpu_switchto \ 43"lwp_t *oldlwp" "lwp_t *newlwp" "bool returning" 44.\" ------------------------------------------------------------ 45.Sh DESCRIPTION 46The 47.Fn cpu_switchto 48function saves the context of the 49.Tn LWP 50which is currently running on the processor, 51and restores the context of the 52.Tn LWP 53specified by 54.Fa newlwp . 55.Pp 56Remarks: 57.Bl -enum -offset indent 58.It 59.Fn cpu_switchto 60does not switch address spaces. 61.It 62.Fn cpu_switchto 63sets 64.Xr curlwp 9 65to 66.Fa newlwp . 67If the architecture does non-interlocked adaptive mutex release, 68.Fn cpu_switchto 69does an equivalent of 70.Xr membar_producer 3 , 71before and after the modification of 72.Xr curlwp 9 . 73.It 74.Fn cpu_switchto 75should be called at 76.Dv IPL_SCHED . 77When the function returns, the caller should lower 78the priority level as soon as possible. 79.It 80.Fn cpu_switchto 81might be called with spin mutexes held. 82.El 83.Pp 84The function takes the following arguments. 85.Bl -tag -width "returning " -offset indent 86.It Fa oldlwp 87Specify the 88.Tn LWP 89from which the switch is going to be made, i.e., the calling 90.Tn LWP . 91If it was 92.Dv NULL , 93the context of the 94.Tn LWP 95currently running on this processor is not saved. 96.It Fa newlwp 97Specify the 98.Tn LWP 99to which to switch. 100It must not be 101.Dv NULL . 102.It Fa returning 103Only meaningful if the architecture implements fast software interrupts. 104If true, it indicates that 105.Fa oldlwp 106is a soft interrupt 107.Tn LWP 108that is blocking. 109It is a good indication that any kind of address space or user activity 110can be completely ignored. 111For example: 112.Xr ras_lookup 9 , 113cache flushes, TLB wirings, adjusting lazy 114.Tn FPU 115state. 116All that is required is to restore the register state and stack, and 117return to the interrupted 118.Tn LWP . 119.El 120.\" ------------------------------------------------------------ 121.Sh RETURN VALUES 122The 123.Fn cpu_switchto 124function does not return until another 125.Tn LWP 126calls 127.Fn cpu_switchto . 128It returns the 129.Vt oldlwp 130argument of the 131.Fn cpu_switchto 132which is called to switch back to our 133.Tn LWP . 134It is either a 135.Tn LWP 136which called 137.Fn cpu_switchto 138to switch to us or 139.Dv NULL 140in case the 141.Tn LWP 142was exiting. 143.\" ------------------------------------------------------------ 144.Sh SEE ALSO 145.Xr membar_producer 3 , 146.Xr swapcontext 3 , 147.Xr intro 9 , 148.Xr mutex 9 , 149.Xr spl 9 150