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Subject: Re: Source code to measure it - results

Author: Keith Evans

Date: 21:44:34 07/15/03

Go up one level in this thread


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?



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