.\"     $NetBSD: cpu_need_resched.9,v 1.9 2011/10/24 07:30:29 yamt Exp $
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.\" by Gregory McGarry.
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.Dd July 31, 2010
.Dt CPU_NEED_RESCHED 9
.Os
.Sh NAME
.Nm cpu_need_resched
.Nd context switch notification
.Sh SYNOPSIS
.In sys/cpu.h
.Ft void
.Fn cpu_need_resched "struct cpu_info *ci" "int flags"
.Sh DESCRIPTION
The
.Fn cpu_need_resched
function is the machine-independent interface for the scheduler to
notify machine-dependent code that a context switch from the current
LWP, on the cpu
.Fa ci ,
is required.
This event may occur if a higher priority LWP appears on the run
queue or if the current LWP has exceeded its time slice.
.Pp
If
.Dv RESCHED_KPREEMPT
flag is specified in
.Fa flags
and
.Dv __HAVE_PREEMPTION
C pre-processor macro is defined in
.In machine/intr.h ,
machine-dependent code should make a context switch happen as soon as possible
even if the cpu is running the kernel code.
.Pp
If
.Dv RESCHED_IMMED
flag is specified in
.Fa flags ,
machine-dependent code should make a context switch happen as soon as possible.
In that case, for example, if
.Fa ci
is not the current processor,
.Fn cpu_need_resched
typically issues an inter processor call to the processor to make it
notice the need of a context switch as soon as possible.
.Pp
Typically, the
.Fn cpu_need_resched
function will perform the following operations:
.Bl -bullet -offset indent
.It
Set a per-processor flag which is checked by
.Xr userret 9
when returning to user-mode execution.
.It
Post an asynchronous software trap
.Pq Tn AST .
.It
Send an inter processor interrupt to wake up
.Xr cpu_idle 9 .
.El
.Sh SEE ALSO
.Xr sched_4bsd 9 ,
.Xr userret 9