Date: Tue, 09 Mar 2004 19:20:33 -0600 (CST) From: Conrad Sabatier <conrads@cox.net> To: Jon Noack <noackjr@alumni.rice.edu> Cc: freebsd-current@freebsd.org Subject: Re: APIC/SMP on UP? (was Re: Load average with CURRENT) Message-ID: <XFMail.20040309192033.conrads@cox.net> In-Reply-To: <404DFE26.5060007@alumni.rice.edu>
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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@cox.net> - "In Unix veritas"
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