[erlang-questions] widefinder update

David Hopwood <>
Mon Oct 29 01:26:09 CET 2007


Anders Nygren wrote:
> On 10/28/07, Thomas Lindgren <> wrote:
>
>> In this particular case, you could increase I/O
>> performance by, say, striping the disk. And you can
>> increase CPU performance by, say, distributing the
>> work to multiple hosts/nodes (fairly straightforward
>> with Erlang, by the way). But with these problems,
>> even with infinite hardware you will eventually run
>> into some sequential portion of the code, and that
>> will limit the speedup as per Amdahl's Law.
> 
> Currently that sequential part is ~ 0.5s on my 1.66GHz
> dual core laptop. the part of the work that can be run in parallel
> takes ~2.254 s so theoretically we would get
> Cores  Real time  Speedup  Rel. speedup by doubling #cores
[...]
>   8      0.782     3.523      1.360
[...]
> 256      0.509     5.413      1.017
> 
> Which is not very good after 8 cores.

0.5 s is not very long, in human terms. For me to be convinced that
there is any need for further optimization, the problem would have
to be scaled to a point where the total run-time is something that
a human might conceivably get impatient waiting for. At that point,
the sequential part would likely be a smaller proportion of the
run-time anyway.

-- 
David Hopwood <>




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