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SMP(4)		       FreeBSD Kernel Interfaces Manual			SMP(4)

NAME
     SMP -- description	of the FreeBSD Symmetric Multi-Processor kernel

SYNOPSIS
     options SMP

DESCRIPTION
     The SMP kernel implements symmetric multi-processor support.

COMPATIBILITY
     Support for multi-processor systems is present for	all Tier-1 architec-
     tures on FreeBSD.	Currently, this	includes alpha,	amd64, i386, ia64, and
     sparc64.  Support is enabled using	options	SMP.  It is permissible	to use
     the SMP kernel configuration on non-SMP equipped motherboards.

I386 NOTES
     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 device apic.	 The mptable(1)	command	may be used to view
     the status	of multi-processor support.

     The number	of CPUs	detected by the	system is available in the read-only
     sysctl variable hw.ncpu.

     FreeBSD allows specific CPUs on a multi-processor system to be disabled.
     The sysctl	variable machdep.hlt_cpus is an	integer	bitmask	denoting CPUs
     to	halt, counting from 0.	Setting	a bit to 1 will	result in the corre-
     sponding CPU being	disabled.

     FreeBSD 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
     machdep.hlt_logical_cpus sysctl to	one.

SEE ALSO
     mptable(1), sysctl(8), condvar(9),	msleep(9), mtx_pool(9),	mutex(9),
     sema(9), sx(9)

HISTORY
     The SMP kernel's early history is not (properly) recorded.	 It was	devel-
     oped 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 primi-
     tives, 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.

AUTHORS
     Steve Passe <fsmp@FreeBSD.org>

FreeBSD	10.1		       December	17, 2004		  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | COMPATIBILITY | I386 NOTES | SEE ALSO | HISTORY | AUTHORS

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