Steve Passe <fsmp@FreeBSD.ORG>. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. The name of the developer may NOT be used to endorse or promote products
derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
$FreeBSD: head/share/man/man4/smp.4 138999 2004-12-18 01:13:37Z jkoshy $
.Dd December 17, 2004 .Dt SMP 4 .Os .Sh NAME .Nm SMP .Nd description of the FreeBSD Symmetric Multi-Processor kernel .Sh SYNOPSIS .Cd options SMP .Sh DESCRIPTION The .Nm kernel implements symmetric multi-processor support. .Sh COMPATIBILITY Support for multi-processor systems is present for all Tier-1 architectures on .Fx . Currently, this includes alpha, amd64, i386, ia64, and sparc64. Support is enabled using .Cd options SMP . It is permissible to use the SMP kernel configuration on non-SMP equipped motherboards. .Sh I386 NOTES For i386 systems, the .Nm kernel supports motherboards that follow the Intel MP specification, version 1.4. In addition to .Cd options SMP , i386 also requires .Cd device apic . The .Xr mptable 1 command may be used to view the status of multi-processor support.
p The number of CPUs detected by the system is available in the read-only sysctl variable .Va hw.ncpu .
p .Fx allows specific CPUs on a multi-processor system to be disabled. The sysctl variable .Va machdep.hlt_cpus is an integer bitmask denoting CPUs to halt, counting from 0. Setting a bit to 1 will result in the corresponding CPU being disabled.
p .Fx supports hyperthreading on Intel CPU's on the i386 platform. Since using logical CPUs can cause performance penalties under certain loads, the logical CPUs can be disabled by setting the .Va machdep.hlt_logical_cpus sysctl to one. .Sh SEE ALSO .Xr mptable 1 , .Xr sysctl 8 , .Xr condvar 9 , .Xr msleep 9 , .Xr mtx_pool 9 , .Xr mutex 9 , .Xr sema 9 , .Xr sx 9 .Sh HISTORY The .Nm kernel's early history is not (properly) recorded. It was developed in a separate CVS branch until April 26, 1997, at which point it was merged into 3.0-current. By this date 3.0-current had already been merged with Lite2 kernel code.
p .Fx 5.0 introduced support for a host of new synchronization primitives, and a move towards fine-grained kernel locking rather than reliance on a Giant kernel lock. The SMPng Project relied heavily on the support of BSDi, who provided reference source code from the fine-grained SMP implementation found in sx .
p .Fx 5.0 also introduced support for SMP on the alpha, ia64, and sparc64 architectures. .Sh AUTHORS .An Steve Passe Aq fsmp@FreeBSD.org