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Date: Fri, 30 Nov 2007 16:42:09 +0100
From: Kris Kennaway <kris@FreeBSD.org>
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To: Pete French <petefrench@ticketswitch.com>
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Cc: max@love2party.net, freebsd-stable@freebsd.org, kometen@gmail.com
Subject: Re: Also seeing 2 x quad-core system slower that 2 x dual core
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Pete French wrote:
>> Yes, if the claim is that the hardware is absolutely identical apart 
>> from one having two quad-core CPUs instead of two dual-core, the next 
>> step is to disable half of the CPUs and confirm that the problem goes away.
> 
> Just comming back to this today, will do a side by side compare of the dmesg
> later to make sure that they *are* identical as claimed, but the idea of
> disabling half the CPU's is an excellent one!
> 
> Aha, brilliant idea!
> 
>> Check dmesg for the APIC numbers corresponding to the CPUs you want to 
>> disable and add the corresponding entries to /boot/loader.conf, e.g.:
> 
> You mean this bit?
> 
> FreeBSD/SMP: Multiprocessor System Detected: 8 CPUs
>  cpu0 (BSP): APIC ID:  0
>  cpu1 (AP): APIC ID:  1
>  cpu2 (AP): APIC ID:  2
>  cpu3 (AP): APIC ID:  3
>  cpu4 (AP): APIC ID:  4
>  cpu5 (AP): APIC ID:  5
>  cpu6 (AP): APIC ID:  6
>  cpu7 (AP): APIC ID:  7
> 
>> hint.lapic.1.disable="1"
>> hint.lapic.3.disable="1"
>> hint.lapic.5.disable="1"
>> hint.lapic.7.disable="1"
> 
> gives me...
> 
> hint.lapic.1.disable="1"
> hint.lapic.3.disable="3"
> hint.lapic.5.disable="5"
> hint.lapic.7.disable="7"
> 
> rebooting now to give it a try...

Well, the "1" is a boolean so those values will probably also work, but 
the point was to disable apics 1,3,5 and 7 on the left hand side :)  In 
your case those are also valid but sometimes they are other numbers.

Kris