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Subject: Re: Pentium 4 and hyperthreading (to Charles Worthington)

Author: Steffen Basting

Date: 13:41:09 02/19/03

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On February 19, 2003 at 16:18:54, Charles Worthington wrote:

>On February 19, 2003 at 16:13:58, Steffen Basting wrote:
>
>>Hi!
>>No, I would say Martin is right. You can do that with rather practical numbers:
>>
>>One processor, ht disabled: 1.000 nps.
>>=> Two processors, ht disabled: 2.000 nps.
>>
>>One processor, ht enabled: 1160 nps (ht disabled + 16%).
>>=> Two processors, ht enabled: 2.320 nps.
>>
>>and 2.000 * 1.16 = 2.320, so your speed up is 16% for both cpus.
>>
>>
>>Regards, Steffen
>
>
>actally the speedup is doubled when you are dealing with dual processors. You
>are using reverse mathematics to arrive at an incorrect answer. I honestly think
>Dr. Hyatt knows his math.

There's no doubt that Dr. Hyatt knows his math - I just cannot see the "bug" in
my example. If the speed-up increases in the way you describe (n proc * 16%), it
would mean that with 16 processors ht enabled you arrive at 256%. So you are
faster than > 32 processors with ht disabled. This doesn't seem to be correct...

Regards, Steffen



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