SMP -- description of the FreeBSD Symmetric MultiProcessor kernel
options SMP
The SMP kernel implements symmetric multiprocessor support.
Support for multi-processor systems is present for all Tier-1 architectures
on FreeBSD. Currently, this includes alpha, i386, ia64, and
sparc64. Support is enabled using options SMP. On most platforms it is
permissible to use the SMP kernel configuration on non-SMP equipped motherboards.
The only exception to this rule is the i386 platform.
For i386 systems, the SMP kernel supports motherboards that follow the
Intel MP specification, version 1.4. In addition to options SMP, i386
also requires options APIC_IO. The mptable(1) command may be used to
view the status of multi-processor support.
FreeBSD supports hyperthreading on Intel CPU's on the i386 platform. By
default, logical CPUs are not used to execute user processes due to performance
penalties under common loads. To allow the logical CPUs to execute
user processes, turn off the machdep.hlt_logical_cpus sysctl by setting
its value to zero.
mptable(1), condvar(9), msleep(9), mtx_pool(9), mutex(9), sema(9), sx(9)
The SMP 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.
FreeBSD 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 BSD/OS.
FreeBSD 5.0 also introduced support for SMP on the alpha, ia64, and
sparc64 architectures.
Steve Passe <fsmp@FreeBSD.org>
FreeBSD 5.2.1 December 5, 2002 FreeBSD 5.2.1 [ Back ] |
