.\" Copyright (c) 2005 Robert N. M. Watson
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD: head/share/man/man4/sched_4bsd.4 206622 2010-04-14 19:08:06Z uqs $
.\"
.Dd January 21, 2008
.Dt SCHED_4BSD 4
.Os
.Sh NAME
.Nm sched_4bsd
.Nd "4.4BSD scheduler"
.Sh SYNOPSIS
.Cd "options SCHED_4BSD"
.Sh DESCRIPTION
The
.Nm
scheduler
is the traditional system scheduler, providing both high throughput and solid
interactive response in the presence of load.
.Pp
The following sysctls are relevant to the operation of
.Nm :
.Bl -tag -width indent
.It Va kern.sched.name
This read-only sysctl reports the name of the active scheduler.
.It Va kern.sched.quantum
This read-write sysctl reports or sets the length of the quantum (in
micro-seconds) granted to a thread.
.It Va kern.sched.ipiwakeup.enabled
This read-write sysctl sets whether or not the scheduler will generate an
inter-processor interrupt (IPI) to an idle CPU when a thread is woken up.
Otherwise, idle CPUs will wait until the next clock tick before looking for
new work.
.It Va kern.sched.preemption
This read-only sysctl reports whether or not the kernel is configured to
support preemption, which reduces the latency to run lower priority threads
on wakeup.
.El
.Pp
Some sysctls will be available only on systems supporting SMP.
.Sh SEE ALSO
.Xr sched_ule 4 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
scheduler has been present, in various forms, since the inception of
.Bx .
.Sh BUGS
While a highly robust and time-tested scheduler,
.Nm
lacks specific knowledge of how to schedule advantageously in non-symmetric
processor configurations, such as hyper-threading.