linux-kernel - Re: How to detect multi-core and/or HT-enabled CPUs in 2.4.x and 2.6.x kernels

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Message-Id: <1167234806.3281.3966.camel@laptopd505.fenrus.org>
Date:	Wed, 27 Dec 2006 16:53:26 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	knobi@...bisoft.de
Cc:	Gleb Natapov <glebn@...taire.com>, linux-kernel@...r.kernel.org
Subject: Re: How to detect multi-core and/or HT-enabled CPUs in 2.4.x and
	2.6.x kernels


>  
>  this is a real interesting question. Ganglia is coming [originally]
> from the HPC side of computing. At least in the past HT as implemented
> on XEONs did help a lot. Running two CPU+memory-bandwith intensive
> processes on the same physical CPU would at best result in a 50/50
> performance split. So, knowing how many "real" CPUs are in a system is
> interesting to us.

but this 50/50 split is most likely because of either a cache or a
bandwidth bottleneck, at which point "HT" is the wrong measure.

(also if you go to things like SUN's Niagara CPU then it's even more
clear that SMT isn't the right measure for performance capability)


-- 
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