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Subject: Re: Source code to measure it - results

Author: Robert Hyatt

Date: 20:35:30 07/15/03

Go up one level in this thread

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.

>That's what i'm after of course.
>Apart from a bug in the RNG i need to point that RAM factors could also play a
>role here. Like the distance signals need to carry in the RAM. If that's not the
>problem but the RNG is the problem then definitely it is the case that i would
>encourage you to find a better RNG or a modification to this RNG so that it
>works better for small hashsizes.
>For now i just conclude that it is a fact that the 130 ns figures is *not* even
>close to the times that we need to do a lookup in the hashtable at a dual Xeon
>133Mhz DDR ram which bob has. It's quite a bit closer to 400ns in fact :)

It is _exactly_ 150ns +/- 1ns.  No more, no less.

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