[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [f-cpu] RC5, F-CPU and srotl



Yann Guidon a écrit :
<...>
> > > > but it can handle large working sets. Therefore
> > > > I'd rather focus on scientific applications, databases and so on.
> > > don't worry, this will follow naturally, but how many scientists do you
> > > know around F-CPU ?...
> > Do I have to *know* them? ;)
> that can help.
> 
> For example, a CFD scientist has explained me how the newest algos
> work, and they WILL benefit from very wide SIMD cores (contrarily
> to what nicO said). the limiting factor is of course the RAM bandwidth,
> as it deals with gigabytes of 3D data... but i have developped
> a strip-mining stategy that helps :-)
> 
<troll detector == 100%>

I don't know what you mean about CFD scientist. I imagine that it is
always possible to change dependancies inside an algorythme by using a
temporary array. So you break a strong dependancies, but you increase
(double ?) the memory bandwith demand.

Never forget that fcpu need to performe well in a vast majority of task
and writing specific code for fcpu will represente less than 1% of the
code.

If your compiler didn't know how to change your algorythme to use
special trick, this trick aren't usefull at all. Nobody will rewrite
millions man.hours of code soon made. 

The limit of ~256 bit (paquet of 64 bit floating point register) are
fixed by using a new vectorising technique on the programme used in the
spec benchmark. This program are real world one and fcpu will be judged
in front of such benchmark. If the couple compiler+fcpu couldn't use
efficently more than 256 bits, it will be unreallistic to use it from an
economical point of view for only very few specific program.

(If you ever used scp instead of ftp to transfert datas you will
understood why fast encryption are needed.)

nicO
*************************************************************
To unsubscribe, send an e-mail to majordomo@seul.org with
unsubscribe f-cpu       in the body. http://f-cpu.seul.org/