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From: Ivan Voras <ivoras@freebsd.org>
Date: Wed, 10 Nov 2010 12:20:45 +0100
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Cc: freebsd-smp@freebsd.org
Subject: Re: kern.smp.topology
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On 11/10/10 11:56, Ivan Klymenko wrote:
> Hello! People.
> 
> Who can explain the purpose of sysctl variable kern.smp.topology?
> What does it affect?
> 
> It may take such values:
> 1      -Dual core with no sharing.
> 2      -No topology, all cpus are equal.
> 3      -Dual core with shared L2.
> 4      -quad core, shared l3 among each package, private l2.
> 5      -quad core,  2 dualcore parts on each package share l2.
> 6      -Single-core 2xHTT
> 7      -quad core with a shared l3, 8 threads sharing L2.
> default-Default, ask the system what it wants.
> 
> Does it make sense to set its value manually, if I know that my CPU Core2Duo?
> How to do this, select a value?
> 
> I not found this explanation in any of the official guides ...

Short answer is: you should not have to touch it, ever.

Long answer: it's used mostly for testing ULE and debugging
topology-related problems. It's even less relevant in recent kernels (9,
8-stable) where a better topology parser has been committed.