sched_4bsd(4)

NAME

sched_4bsd - 4.4BSD scheduler

SYNOPSIS

options SCHED_4BSD

DESCRIPTION

The sched_4bsd scheduler is the default system scheduler,

providing both
high throughput and solid interactive response in the pres

ence of load.

The following sysctls are relevant to the operation of

sched_4bsd:

kern.sched.name

This read-only sysctl reports the name of the active

scheduler.

kern.sched.quantum

This read-write sysctl reports or sets the length of

the quantum
(in micro-seconds) granted to a thread.

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.

kern.sched.preemption

This read-only sysctl reports whether or not the

kernel is configured to support preemption, which reduces the la

tency to run
lower priority threads on wakeup.

Some sysctls will be available only on systems supporting

SMP.

SEE ALSO

sched_ule(4), sysctl(8)

HISTORY

The sched_4bsd scheduler has been present, in various forms,

since the
inception of BSD.

BUGS

While a highly robust and time-tested scheduler, sched_4bsd

lacks specific knowledge of how to schedule advantageously in non

symmetric processor configurations, such as hyper-threading.

BSD April 7, 2005

BSD