Bug 17346

Summary:	APIC cannot be enabled without turning on support for SMP
Product:	Base System	Reporter:	aron <aron>
Component:	i386	Assignee:	freebsd-bugs (Nobody) <bugs>
Status:	Closed FIXED
Severity:	Affects Only Me
Priority:	Normal
Version:	Unspecified
Hardware:	Any
OS:	Any

Description aron 2000-03-12 20:20:01 UTC

The FreeBSD kernel only supports enabling the APIC when SMP support
is configured in the kernel. APICs are desirable even in uniprocessor
systems because they provide 1) on chip timers 2) larger number of IRQs
and 3) low interrupt overheads. Unfortunately, if the FreeBSD kernel
is compiled with SMP support, the performance drops down - possibly
due to the various locking mechanisms that get turned on. A webserver's
performance drops down by 22% when SMP support is turnedon a an otherwise
uniprocessor machine.

Fix: 

The FreeBSD kernel should support turning on the APIC without turning
on SMP support. This is useful in uniprocessor systems.
How-To-Repeat: Trying compiling the kernel after turning on the option APIC_IO in 
the kernel configuration file. Make sure that the option SMP is not 
turned on. Kernel wouldn't compile.

Comment 1 Mike Barcroft freebsd_committer

2001-07-22 01:17:31 UTC

State Changed
From-To: open->closed


This PR addresses a general problem with SMP.  That it is slower 
under some circumstances.  5.0-RELEASE should fix this; thereby 
resolving this PR.