Re: [Chicken-users] anyone have a Playstation 3 ?

[Brandon J. Van Every]

Shawn Rutledge wrote:
> On 12/20/06, Brandon J. Van Every <address@hidden> wrote:
> > I seriously doubt that the best way to make use of all those Cell
> > processing units is with any kind of threading.  I expect there's
> > probably some way to more tightly synchronize their actions, when coding
> > hand assembly.  I'm not interested in the Cell as some kind of
> > architecture where you just forget about what you're doing, put stuff in
> > threads, and hope they perform better.  That's how the XBox 360 is
> > designed; its threading model is coarse and conventional.  I'm sure it
> > will be popular with developers that don't want to think much about the
> > architecture.  I expect, however, that the Cell has capabilities that
> > can only be realized by writing very specifically for that
> > architecture.  I haven't read up on the Cell enough to know what is
> > possible, but I will be doing so.
>
> Yeah, makes sense.
>
> What other kinds of constructs can you imagine in Scheme for parallel
> execution, which would work better than threads?

Well I really don't think in Scheme yet, to be honest.  I think in 
assembly code and arrays.  I'm interested in AI terrain analysis 
problems for Civilization-style game maps.  I would look at how to 
parallelize the analysis of such a map.  I'd assume that I have all 8 
SPEs available to me to do so, and that my algorithm is in charge of 
synchronizing them.

I would probably try to give each SPE a large, fixed quantity of work, 
so that I know when the SPE will terminate its work.  I call these "one 
size fits all" algorithms.  For instance, rather than write a bunch of 
special cases for 3D matrix transforms, based on whether you've got a 
3x3 matrix, or a 4x3 with a "1" coefficient in the corner, and all this 
other stuff, you just code a 4x4 matrix and always use that, even for a 
2x2 matrix.  On a DEC Alpha in 1996, the 4x4 solution wasn't any slower 
than the 2x2 solution, due to the realities of instruction pipeline 
delays.  I was doing the 4x4 in 16 clocks.  The benefit of a "one size 
fits all" algorithm is you don't waste time on conditional branching, 
trying to decide what kind of case you're optimizing.  Also, the code is 
faster to implement and easier to maintain, because you're only doing 1 
thing.

I'll also be interested in "optimizing other people's problems," 
particularly 3D graphics problems, because that's where I anticipate the 
money will be.  To me, this is more about looking at what you can do 
with an extant codebase.  I don't think, as a $$$$$ consulting service, 
that I'm often going to get the chance to design a "from scratch" 
architecture.  Rather, someone will have written a bunch of "normal" 
code for, say, a PC, a XBox, or perhaps a data server (i.e. nascent 
BladeServer QS20 market).  Then they'll try to port to the Cell, have 
problems, and say "WTF is going on??!?"  I anticipate that the solutions 
to such problems are going to be ad hoc and based in engineering 
pragmatism, i.e. best performance improvement for modest amount of 
consulting dollars spent.  In short, doing what compilers cannot 
typically bring themselves to do.   So part of that drill, will be 
learning what the IBM compilers are actually capable of.  I doubt 
they're as stupid as Microsoft compilers; man, those have always been 
really boring to work with.  Code optimization has never been 
Microsoft's profit center when working on their compiler products.  I 
never really got into Intel compilers.  I heard they were better, but 
they cost $$$, and it's not very exciting to try to optimize for x86 
anyways.  Not much scope for doing anything.


> Today there was also this article:
>
> http://tech.blorge.com/Structure:%20/2006/12/25/people-swapping-ps3s-for-wiis/ 

Some guy working at some game store wrote something on some forum 
somewhere.  He said, at his store, they'd get 30 Wiis in and sell 'em 
out rapidly.  They'd get 2 PS3s in and 1 would still be sitting on the 
shelf at the end of the day.  So it seems the difficulty of obtaining a 
PS3 will rapidly be over with. 


Cheers,
Brandon Van Every