.\" Copyright (c) 2005 Robert N. M. Watson
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.\" $FreeBSD$
.\"
.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.