/share/man/man4/sched_4bsd.4

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25.\" $FreeBSD$
26.\"
27.Dd January 21, 2008
28.Dt SCHED_4BSD 4
29.Os
30.Sh NAME
31.Nm sched_4bsd
32.Nd "4.4BSD scheduler"
33.Sh SYNOPSIS
34.Cd "options SCHED_4BSD"
35.Sh DESCRIPTION
36The
37.Nm
38scheduler
39is the traditional system scheduler, providing both high throughput and solid
40interactive response in the presence of load.
41.Pp
42The following sysctls are relevant to the operation of
43.Nm :
44.Bl -tag -width indent
45.It Va kern.sched.name
46This read-only sysctl reports the name of the active scheduler.
47.It Va kern.sched.quantum
48This read-write sysctl reports or sets the length of the quantum (in
49micro-seconds) granted to a thread.
50.It Va kern.sched.ipiwakeup.enabled
51This read-write sysctl sets whether or not the scheduler will generate an
52inter-processor interrupt (IPI) to an idle CPU when a thread is woken up.
53Otherwise, idle CPUs will wait until the next clock tick before looking for
54new work.
55.It Va kern.sched.preemption
56This read-only sysctl reports whether or not the kernel is configured to
57support preemption, which reduces the latency to run lower priority threads
58on wakeup.
59.El
60.Pp
61Some sysctls will be available only on systems supporting SMP.
62.Sh SEE ALSO
63.Xr sched_ule 4 ,
64.Xr sysctl 8
65.Sh HISTORY
66The
67.Nm
68scheduler has been present, in various forms, since the inception of
69.Bx .
70.Sh BUGS
71While a highly robust and time-tested scheduler,
72.Nm
73lacks specific knowledge of how to schedule advantageously in non-symmetric
74processor configurations, such as hyper-threading.