1.\" Copyright (c) 2005 Robert N. M. Watson 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.Dd January 21, 2008 26.Dt SCHED_4BSD 4 27.Os 28.Sh NAME 29.Nm sched_4bsd 30.Nd "4.4BSD scheduler" 31.Sh SYNOPSIS 32.Cd "options SCHED_4BSD" 33.Sh DESCRIPTION 34The 35.Nm 36scheduler 37is the traditional system scheduler, providing both high throughput and solid 38interactive response in the presence of load. 39.Pp 40The following sysctls are relevant to the operation of 41.Nm : 42.Bl -tag -width indent 43.It Va kern.sched.name 44This read-only sysctl reports the name of the active scheduler. 45.It Va kern.sched.quantum 46This read-write sysctl reports or sets the length of the quantum (in 47micro-seconds) granted to a thread. 48.It Va kern.sched.ipiwakeup.enabled 49This read-write sysctl sets whether or not the scheduler will generate an 50inter-processor interrupt (IPI) to an idle CPU when a thread is woken up. 51Otherwise, idle CPUs will wait until the next clock tick before looking for 52new work. 53.It Va kern.sched.preemption 54This read-only sysctl reports whether or not the kernel is configured to 55support preemption, which reduces the latency to run lower priority threads 56on wakeup. 57.El 58.Pp 59Some sysctls will be available only on systems supporting SMP. 60.Sh SEE ALSO 61.Xr sched_ule 4 , 62.Xr sysctl 8 63.Sh HISTORY 64The 65.Nm 66scheduler has been present, in various forms, since the inception of 67.Bx . 68.Sh BUGS 69While a highly robust and time-tested scheduler, 70.Nm 71lacks specific knowledge of how to schedule advantageously in non-symmetric 72processor configurations, such as hyper-threading. 73