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Subject: Re: Odd hyperthreading behavior

Author: Gian-Carlo Pascutto

Date: 18:49:48 10/04/03

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On October 04, 2003 at 21:40:59, Tom Kerrigan wrote:

>(Quick aside: very shortly after HT first came out, a patch for Linux was
>released to "support" HT--the purpose was not to allow you to use the extra
>logical processors (because they're transparent to the OS) but to solve exactly
>the problem you mention.

2.6.x is the first kernel to have improvements in this regard,
meaning that all normal Linux systems do _not_ have this
optimization yet.

>I assume Microsoft also made a similar fix and I don't
>know which versions of Windows have it, but I am running a version of Windows
>that would.)

You don't know, but you do know?

>Given that, HT would have to be providing a 50% speedup for my program if it
>were only running on one processor, which seems unrealistically high, and that
>also means my program should run 100% faster with 4 threads (vs. 2) but in
>reality it only runs 15% faster.

I don't get your math.

--
GCP



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