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Date: Wed, 30 Mar 2005 10:48:50 +0200
From: Adrien Plisson <aplisson-news@stochastique.net>
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Subject: Re: Gnat 3.15p & Windows & Hyperthreading Q
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Date: 2005-03-30T10:48:50+02:00
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Wiljan Derks wrote:
> The only advantage that hyper threading has, is that the system might be 
> more responsive.
> Thus when accidentally locking one CPU at high priority, one can still break 
> into the system (using the other CPU).

ok, let's release some misconceptions about HyperThreading:
an HyperThreading enabled processor DOES NOT have 2 cores.

it's not clear at all when you look at Intel's overview of 
HyperThreading. they really like to tell it runs as if it were 2 
processors. this may look like true for simple office tasks, which are 
not computationnally intensive. unfortunately, for software 
developpers used to multitasking and trying to get the most of their 
system, it is evident that it is NOT 2 processors.

actually, an HT processor has one core, which makes it no faster than 
a single processor. what's different is that it has 2 sets of 
"states", allowing for more efficient context switches. as noted by 
Wiljan, this makes the system more responsive.

but this paper does explain it in more details:
http://www.intel.com/business/bss/products/hyperthreading/server/ht_server.pdf

-- 
rien