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Subject: Re: Another memory latency test

Author: Gerd Isenberg

Date: 13:11:33 07/17/03

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>Vincent: 256 ns
>Note, random access is faster than before
>I get similar numbers for smaller sizes bigger than the cache
>
>
>Summary: There is more, than just an lmbench number. Actually
>the comment in lmbench source suggests, that they actually
>wanted to get the random access times.
>
>I don't want to argue about defenition of the "real" memory
>latency. But for chess programs/hash the Vinent type number
>is the most interesting.
>
>Regards,
>Dieter

very interesting Dieter,

your algorithm confirms roughly Vincent's results!
I will try it later at home and learn from your source code ;-)
But there is still the question whether this measured times is memory latency
per definition - i guess not.

In worst cases there is more than memory latency (additional TLB-latency and
some RAM hardware interface latencies) to get data into a register - maybe a
question of definition.

Another interesting point is to measure not only the average but the maximum and
minimum access times (processors performance counter?). Are the accesses  about
equal, or are there heavy spikes due to some chaotic TLB behaviour?

Cheers,
Gerd




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