APIC/SMP on UP? (was Re: Load average with CURRENT)

[Conrad Sabatier]

On 09-Mar-2004 Jon Noack wrote:
> On 3/9/2004 10:17 AM, Justin Dossey wrote:
>> On Tue, 9 Mar 2004, Conrad Sabatier wrote:
>>>I've been meaning to ask about this.  Is there anything to be gained on a UP
>>>box by enabling APIC and/or SMP?
>> 
>> I'd say yes, there is.  APIC reduces interrupt overhead and provides
>> an on-chip timer. It also provides better interrupt sharing.
> 
> APIC, yes (see above).  SMP incurs a fairly significant amount of 
> overhead (extra locking, etc.).  I think I heard something a while back 
> about attempts to selectively enable SMP locking at runtime (so that 
> leaving SMP enabled in GENERIC doesn't hurt so much for UP), but then 
> again that might have been a dream... ;-)
> 
> In any case, this is what I run on my UP boxes:
>#options       SMP             # Symmetric MultiProcessor Kernel
> device                apic            # I/O APIC

Interesting.  Thanks!

-- 
Conrad Sabatier <conrads at cox.net> - "In Unix veritas"