[erlang-questions] widefinder update

Hynek Vychodil <>
Tue Oct 30 13:39:45 CET 2007


On 10/29/07, David Hopwood <> wrote:
> Anders Nygren wrote:
> >
> > 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.
>

It's bad point of view. What if you would like do it 100 times? 50s is
still good time in human terms? And what about 20GB instead 200MB? The
serial part will be 50s, it's wrong in human terms again. If you can
change serial part three times down, you made three times faster
solution. That's all. And what about web service? You can use three
times cheaper HW to serve same amount of users. It's not enough? Tim
Brays exercise is not only 200MB ~ 1Mrec, but also 1GB ~ 5Mrec, but in
this case 2.5s is long time in human terms if it will may be Web/UI
response. 1.7s will be better anyway.

--Hynek (Pichi) Vychodil



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