.\"	$NetBSD: kpreempt.9,v 1.3 2010/02/16 19:21:30 rmind Exp $
.\"
.\" Copyright (c)2008 YAMAMOTO Takashi,
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.\" ------------------------------------------------------------
.Dd February 16, 2010
.Dt KPREEMPT 9
.Os
.\" ------------------------------------------------------------
.Sh NAME
.Nm kpreempt
.Nd control kernel preemption
.\" ------------------------------------------------------------
.Sh SYNOPSIS
.In sys/systm.h
.\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
.Ft void
.Fn kpreempt_disable \
"void"
.Ft void
.Fn kpreempt_enable \
"void"
.Ft bool
.Fn kpreempt_disabled \
"void"
.\" ------------------------------------------------------------
.Sh DESCRIPTION
These functions are used to control kernel preemption of the calling LWP.
.Pp
On architectures where kernel preemption is not supported natively, these
functions may still be used.
.Pp
It should be noted that kernel preemption is also disabled when holding
the interrupt priority level above IPL_NONE, e.g. using
.Xr spl 9
or spinning
.Xr mutex 9
calls or holding kernel_lock (indicating that the code is not MT safe).
.Pp
.Fn kpreempt_disable
disables kernel preemption of the calling LWP.
Note that disabling kernel preemption can prevent LWPs with higher priorities
from running.
.Pp
.Fn kpreempt_enable
enables kernel preemption of the calling LWP, which was previously disabled by
.Fn kpreempt_disable .
.Pp
.Fn kpreempt_disable
and
.Fn kpreempt_enable
can be nested.
.Pp
.Fn kpreempt_disabled
returns
.Dv true
if preemption of the calling LWP is disabled.
It is only for diagnostic purpose.
.\" ------------------------------------------------------------
.\" .Sh RETURN VALUES
.\" ------------------------------------------------------------
.Sh SEE ALSO
.Xr intro 9 ,
.Xr mutex 9 ,
.Xr spl 9