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

From: Brandon J. Van Every
Subject: Re: [Chicken-users] anyone have a Playstation 3 ?
Date: Mon, 25 Dec 2006 22:55:21 -0800
User-agent: Thunderbird (Windows/20061207)

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:

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.

Brandon Van Every

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