.\"	$NetBSD: cpu_switchto.9,v 1.9 2008/01/24 23:06:10 ad Exp $
.\"
.\" Copyright (c)2007 YAMAMOTO Takashi,
.\" All rights reserved.
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.\" ------------------------------------------------------------
.Dd May 21, 2007
.Dt CPU_SWITCHTO 9
.Os
.\" ------------------------------------------------------------
.Sh NAME
.Nm cpu_switchto
.Nd machine-dependent LWP context switching interface
.\" ------------------------------------------------------------
.Sh SYNOPSIS
.In sys/cpu.h
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft lwp_t *
.Fn cpu_switchto \
"lwp_t *oldlwp" "lwp_t *newlwp" "bool returning"
.\" ------------------------------------------------------------
.Sh DESCRIPTION
.Fn cpu_switchto
saves the context of the LWP which is currently running on the processor,
and restores the context of the LWP specified by
.Fa newlwp .
.Pp
.Fn cpu_switchto
doesn't switch address spaces.
.Pp
.Fn cpu_switchto
sets
.Dv curlwp
to
.Fa newlwp .
.Pp
.Fn cpu_switchto
should be called at
.Dv IPL_SCHED .
When
.Fn cpu_switchto
returns, the caller should lower the priority level as soon as possible.
.Pp
.Fn cpu_switchto
might be called with spin mutexes held.
.Pp
It takes the following arguments.
.Bl -tag -width oldlwp
.It Fa oldlwp
Specify the lwp from which we are going to switch, i.e.,
the calling LWP.
If it was
.Dv NULL ,
the context of the LWP currently running on this processor is not saved.
.It Fa newlwp
Specify the lwp to which we are going to switch.
It must not be
.Dv NULL .
.It Fa returning
Only meaningful if the architecture implements fast software interrupts.
If true, it indicates that
.Fa oldlwp
is a soft interrupt LWP that is blocking.
It's a good indication that any kind of address space or user activity
can be completely ignored.
For example: ras_lookup(), cache flushes, TLB wirings, adjusting lazy FPU
state.
All that is required is to restore the register state and stack, and
return to the interrupted LWP.
.El
.\" ------------------------------------------------------------
.Sh RETURN VALUES
.Fn cpu_switchto
does not return until another LWP calls
.Fn cpu_switchto
to switch to us.
It returns the
.Dv oldlwp
argument of the
.Fn cpu_switchto
which is called to switch back to our LWP.
It's either an LWP which called
.Fa cpu_switchto
to switch to us or
.Dv NULL
in the case that the LWP was exiting.
.\" ------------------------------------------------------------
.Sh SEE ALSO
.Xr swapcontext 3 ,
.Xr intro 9 ,
.Xr mutex 9 ,
.Xr spl 9