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Fwd: Quote from CACM paper: cost of parallelism

On Sun, Oct 11, 2009 at 7:53 PM, Ruth Ivimey-Cook <ruth.Ivimey-Cook@xxxxxxxxxx> wrote:
Larry Dickson wrote:
Sorry to be a little slow on this, but...

I think the key task for our side is what the previous poster talked about - the Cell processor (and similar). We all know that it should be + EASY + to program the Cell, because it's just a slightly disguised PC and B008 with 8 transputers ;-)  But none of us that I know of, including myself, has actually done anything about this...
I would agree with Eric; the Cell is an interesting design but far from easy to program for. I do seem to recall that someone at Kent did some work with the transterpreter on the Cell. Maybe my memory is faulty.

Damian Dimmich and others did it: http://www.transterpreter.org/publications/pdfs/a-cell-transterpreter.pdf. The success is limited, however.

I tried to port occam directly to the Cell, but didn't get very far. It's quite complicated to program this processor.

And the key is what Rick says, we start from the wrong place. Namely, the mountain of massive OS constructs and their insistence on hiding the "bare metal". The Transputer was a big technical success because it was driven from DOS, a totally minimalistic non-OS that allowed you to go around it and whack away, in standard code, at things like DMA addresses. Now we have to tiptoe around the whole attic full of exploding OS and driver constructs, never doing a real design (like a classic car), and the effort involved is not only triple or more, but discouragingly senseless.

And this is where I get disappointed. While I can see where Larry is coming from (I too appreciated the ability to program on bare metal on the transputer) it is no longer practical with the sorts of systems being designed and the nature of the solutions being demanded because ultimately, you end up having to reinvent the wheel. The OS constructs, in the main, are aimed at (a) supporting legacy apps and (b) providing a kit of parts to make applications easier to write. While I can agree that you can eliminate that in some embedded environments, your can't do so on mainstream desktop OSs, which are the ones feeling the pinch right now.

>From my (these days) very "industrial" view, the place to start is simply where we are - namely, often large apps of mainly C code written by various authors over many years, with tight deadlines and demanding management. Pretending that we have the luxury of redesigning either OS's or the raw silicon is fairy tales, not because we can't see why it might be useful or interesting, but because (in the case of the million-odd line codebase I'm thinking of) it would probably take over 5 years for a competent team of people. We don't have that time to spend, let alone the money to pay people. Moreover, in many cases we are also constrained tightly by our own customers, who say things like "we'd love your code, but it must run on weird processor X using niche compiler Y". We have to be able to write the code using very portable constructs. No gcc-isms here, I'm afraid.

I was hoping, in posting the original email, that people might be able to say "well, if you do things *this* way..."  but it seems not.

At present the general computing world is being forced by the scruff of its neck to face parallel programming head on. I believe it won't be long before even the current luxury of true shared memory will be left behind and we'll all be in NUMA land. For CSP to be part of that new world depends on proponents being able to provide usable solutions to the problems real people face.

A year or so ago, I was hopeful that the CSP community would be ready to take up this challenge, but I'm becoming less hopeful now.