os that rather uses the gpu?

JD jd1008 at gmail.com
Sat Jul 17 02:35:48 UTC 2010

  On 07/16/2010 04:49 PM, Robert Myers wrote:
> On Fri, Jul 16, 2010 at 6:36 PM, Christofer C. Bell 
> <christofer.c.bell at gmail.com <mailto:christofer.c.bell at gmail.com>> wrote:
>     On Thu, Jul 15, 2010 at 10:56 PM, Robert Myers
>     <rbmyersusa at gmail.com <mailto:rbmyersusa at gmail.com>> wrote:
>         This is a technical forum, not a debating society.  Science is
>         awash already in useless flops.
>     You're showing your ignorance, Robert.  FLOPS is a very useful
>     measure and more is always good, but I don't think you know what
>     it means.  It means FLoating Point Operations Per Second.  It's
>     nothing more than a measure of computational speed and says
>     nothing about the accuracy of the models being computed.
>         In one of these long-running public debates, I pointed out to
>         a national decision-maker how relatively meaningless and
>         frequently wrong NOAA's hurricane season predictions have
>         been.  Guess what?  The most recent forecast was wrapped in
>         all kinds of weasel words.  That won't stop them from drawing
>         their paychecks and burning megawatts producing useless pictures.
>     If the forecast is wrong, the either the model was inaccurate or
>     the input data was wrong.  It says absolutely nothing about the
>     value of computing the answer fast (what FLOPS provides).  While I
>     totally get you're going to somehow try to refute the idea that
>     "having a fast computer is good" and thus, I can only imagine,
>     make the case that "a slow computer is even better," you're not
>     going to convince anyone.
> Whether you like it or not, and whether, even more important, you 
> understand it or not, the architecture of a computer has a big impact 
> on the kinds of models you can implement with any degree of efficiency 
> on the computer.  Hanging lots of flops on inadequate bandwidth is 
> popular because you can get a high ranking on the Top 500 list with a 
> minimal expenditure, but it also means that you can't do an important 
> calculation like a global FFT at anything like reasonable efficiency. 
>  Flops are almost free.  Bandwidth is expensive.  Unfortunately, what 
> is almost free (flops) can be nearly useless for, say, an FFT unless 
> you have the bandwidth to move data around globally fast enough.
> Skimping on global bandwidth so that you can't do global operations 
> effectively forces you to approximations that require only local 
> computation, that's the kind of modeling we get, and the fact that 
> there is an inherent disconnect between the way the equations behave 
> and the way the discretized model behaves gets swept under the rug. 
>  Nonlinear systems interact globally at all scales at every time step. 
>  If your discretization scheme forces an inaccurate representation of 
> that global interaction, then you shouldn't ever trust what's coming 
> out of your simulation of nonlinear systems.
> Attempting to simulate hurricanes is about as nonlinear as it gets. 
>  When your weatherman on TV knowingly talks about tropical waves as a 
> cause of concern, he's talking about a large scale flow pattern that 
> might or might not go through some tortuous nonlinear processes that 
> will turn it into a hurricane.  Modelling the interaction of hugely 
> different physical scales accurately is essential to accurate 
> prediction, and modern "supercomputers" are notably and chronically 
> short of the bandwidth required to do so.
>     Anyway, technical forum or not, it's a forum made up of people and
>     that makes it a community.  To get along in a community, it helps
>     to not be an asshole.  While you may not care about being an
>     asshole, do note that "getting along in a community" does
>     influence if anyone takes you seriously.  And you seem very much
>     to want to be taken seriously. 
> Calling other people names helps to build a community?  From your 
> pompous and condescending tone unbacked by actual knowledge, I'd be 
> inclined to label you in the same way you have chosen to label me, 
> with the addition of the word "ignorant" in front of it, but I don't 
> think name-calling and labeling ever helps.
> Robert.

So, what would you say is/are the class/classes of problems that would 
benefit greatly from a high flops gpu, but without the sort of bus 
bandwidth you would like to see?

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