1.\" Copyright (c) 1997 2.\" Steve Passe <fsmp@FreeBSD.ORG>. 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. The name of the developer may NOT be used to endorse or promote products 10.\" derived from this software without specific prior written permission. 11.\" 12.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 13.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 14.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 15.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 16.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 17.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 18.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 19.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 20.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 21.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 22.\" SUCH DAMAGE. 23.\" 24.\" $FreeBSD$ 25.\" 26.Dd December 17, 2004 27.Dt SMP 4 28.Os 29.Sh NAME 30.Nm SMP 31.Nd description of the FreeBSD Symmetric Multi-Processor kernel 32.Sh SYNOPSIS 33.Cd options SMP 34.Sh DESCRIPTION 35The 36.Nm 37kernel implements symmetric multi-processor support. 38.Sh COMPATIBILITY 39Support for multi-processor systems is present for all Tier-1 40architectures on 41.Fx . 42Currently, this includes amd64, i386, ia64, and sparc64. 43Support is enabled using 44.Cd options SMP . 45It is permissible to use the SMP kernel configuration on non-SMP equipped 46motherboards. 47.Sh I386 NOTES 48For i386 systems, the 49.Nm 50kernel supports motherboards that follow the Intel MP specification, 51version 1.4. 52In addition to 53.Cd options SMP , 54i386 also requires 55.Cd device apic . 56The 57.Xr mptable 1 58command may be used to view the status of multi-processor support. 59.Pp 60The number of CPUs detected by the system is available in 61the read-only sysctl variable 62.Va hw.ncpu . 63.Pp 64.Fx 65allows specific CPUs on a multi-processor system to be disabled. 66The sysctl variable 67.Va machdep.hlt_cpus 68is an integer bitmask denoting CPUs to halt, counting from 0. 69Setting a bit to 1 will result in the corresponding CPU being 70disabled. 71.Pp 72.Fx 73supports hyperthreading on Intel CPU's on the i386 platform. 74Since using logical CPUs can cause performance penalties under certain loads, 75the logical CPUs can be disabled by setting the 76.Va machdep.hlt_logical_cpus 77sysctl to one. 78.Sh SEE ALSO 79.Xr mptable 1 , 80.Xr sysctl 8 , 81.Xr condvar 9 , 82.Xr msleep 9 , 83.Xr mtx_pool 9 , 84.Xr mutex 9 , 85.Xr sema 9 , 86.Xr sx 9 87.Sh HISTORY 88The 89.Nm 90kernel's early history is not (properly) recorded. 91It was developed 92in a separate CVS branch until April 26, 1997, at which point it was 93merged into 3.0-current. 94By this date 3.0-current had already been 95merged with Lite2 kernel code. 96.Pp 97.Fx 5.0 98introduced support for a host of new synchronization primitives, and 99a move towards fine-grained kernel locking rather than reliance on 100a Giant kernel lock. 101The SMPng Project relied heavily on the support of BSDi, who provided 102reference source code from the fine-grained SMP implementation found 103in 104.Bsx . 105.Pp 106.Fx 5.0 107also introduced support for SMP on the ia64 and sparc64 architectures. 108.Sh AUTHORS 109.An Steve Passe Aq fsmp@FreeBSD.org 110