device apic on a single processor machine

[John Baldwin]

On Friday 22 October 2004 11:40 am, Mike Tancsa wrote:
> When moving from RELENG_4 to RELENG_5, I noticed that in GENERIC, the
> options
>
> options         SMP             # Symmetric MultiProcessor Kernel
> device          apic            # I/O APIC
>
> are enabled by default.  Going forward, is this the best thing to leave in
> my  default kernel on a uniprocessor machine ? I am not using the ULE
> scheduler either and have hyperthreading disabled in the BIOS.
>
> I did a search on google, and in 2003 it was said not to having either on a
> single processor machine but its not clear if this is no longer the case.

You do want to drop SMP.  As far as 'apic', that is less clear.  If you have 
lots of PCI devices that share interrupts for the !apic case and you do lots 
of interrupt intensive tasks, then 'device apic' might help.  There may also 
be cases where it hurts.  There have been reports that access to the apic 
registers for things like masking sources takes longer than on the 8259As.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org