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Subject: Re: Source code to measure it - results

Author: Robert Hyatt

Date: 07:29:07 07/16/03

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On July 16, 2003 at 00:44:34, Keith Evans wrote:

>On July 16, 2003 at 00:29:43, Robert Hyatt wrote:
>
>>On July 16, 2003 at 00:05:29, Keith Evans wrote:
>>
>>>On July 15, 2003 at 23:35:30, Robert Hyatt wrote:
>>>
>>>>On July 15, 2003 at 23:05:37, Vincent Diepeveen wrote:
>>>>
>>>>>
>>>>>
>>>>>Now i can disproof again the 130ns figure that Bob keeps giving here for dual
>>>>>machines and something even faster than that for single cpu (up to 60ns or
>>>>>something). Then i'm sure he'll be modifying soon his statement something like
>>>>>to "that it is not interesting to know the time of a hashtable lookup, because
>>>>>that is not interesting to know; instead the only scientific intersting thing is
>>>>>to know is how much bandwidth a machine can actually achieve".
>>>>>
>>>>
>>>>
>>>>What is _interesting_ is the fact that you are incapable of even recalling
>>>>the numbers I posted.
>>>>
>>>>to wit:
>>>>
>>>>dual xeon 2.8ghz, 400mhz FSB.  149ns latency
>>>>
>>>>PIII/750 laptop, SDRAM.  125ns.
>>>>
>>>>Aaron posted the 60+ ns numbers for his overclocked athlon.  I assume his
>>>>numbers are as accurate as mine since he _did_ run lm_bench, rather than
>>>>something with potential bugs.
>>>>
>>>>I can post bandwidth numbers if you want, but that has nothing to do with
>>>>latency, as those of us understanding architecture already know.
>>>>
>>>
>>>Can you run lmbench and give the latency numbers for different stride sizes?
>>>Then you could quote numbers from cache,...
>>>
>>
>>Here's my laptop data.  L1 seems to be 4 clocks.  L2 9 clocks, memory
>>at 130ns.  This is a PIII/750mhs machine with SDRAM.  I just ran it again
>>to produce these numbers.
>>
>>
>>
>>Host                 OS   Mhz   L1 $   L2 $    Main mem    Guesses
>>--------- -------------   ---   ----   ----    --------    -------
>>scrappy    Linux 2.4.20   744 4.0370 9.4300       130.2
>>
>>>In the lmbench paper they have a nice graph like this.
>>
>>
>>Is the above what you want?
>
>I think that it's as close as you're going to get. The most important thing is
>that 130 [ns] is the largest number. And wouldn't that be a little bit
>pessimistic even for chess hash tables?


I don't think so, although, in the case of crafty, the actual latency is
about 1/3 of that, since I read three positions and you would ammortize the
latency over those three positions rather than just over one.




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