1.\" $NetBSD: cpu_idle.9,v 1.2 2002/09/27 08:38:58 wiz 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.\" 3. All advertising materials mentioning features or use of this software 18.\" must display the following acknowledgement: 19.\" This product includes software developed by the NetBSD 20.\" Foundation, Inc. and its contributors. 21.\" 4. Neither the name of The NetBSD Foundation nor the names of its 22.\" contributors may be used to endorse or promote products derived 23.\" from this software without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 26.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 27.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 28.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 29.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 30.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 31.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 32.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 33.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 34.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 35.\" POSSIBILITY OF SUCH DAMAGE. 36.\" 37.Dd September 21, 2002 38.Dt CPU_IDLE 9 39.Os 40.Sh NAME 41.Nm cpu_idle 42.Nd idle CPU while waiting for work 43.Sh SYNOPSIS 44.Fd #include \*[Lt]sys/proc.h\*[Gt] 45.Ft void 46.Fn cpu_idle "void" 47.Sh DESCRIPTION 48The 49.Fn cpu_idle 50function is invoked to idle the current CPU while waiting for work to be done. 51It is primarily called by the scheduler if no processes are 52available on the system run queue. 53The 54.Fn cpu_idle 55function is a machine-dependent implementations in order to permit 56low-level CPU control. 57.Pp 58The 59.Fn cpu_idle 60function must be called with the scheduler lock held 61.P see Xr SCHED_LOCK 9 62and at the 63.Xr splsched 9 64interrupt protection level. 65It performs the following operations: 66.Bl -bullet 67.It 68Release the scheduler lock. 69.It 70Lower the current interrupt priority level to permit interrupts to be 71taken that will eventually cause processes to appear again on the 72system run queue. 73.It 74Try to zero some pages for the virtual memory system. 75.It 76Perform any CPU or system power control. 77.It 78Wait until a process appears on the system run queue. 79.It 80Acquire the scheduler lock. 81.El 82.Pp 83For CPUs which don't support an idle operation, the CPU must spin 84until a process appears on the system run queue. 85Generally, this is done by checking if the 86.Va sched_whichqs 87variable in the scheduler is not zero. 88See 89.Xr setrunqueue 9 90for further details. 91.Sh SEE ALSO 92.Xr mi_switch 9 , 93.Xr scheduler 9 , 94.Xr setrunqueue 9 , 95.Xr spl 9 , 96.Xr uvm 9 97