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POWER Processors, SMT and the True Origins of AI
Crow writes "IBM developerWorks has posted an interview with John McCalpin, one of the guys who works on the POWER line of processors. He discusses work on POWER5 (and how the design process works at IBM -- he's also involved in work on the POWER7) and defends the decision that IBM doesn't hand-tune their ICs (as has often been criticized on Ars Technica. Also covers some of the features in the POWER processors, like SMT, the Hypervisor and virtualization -- even addresses the question of whether AIX was designed by space aliens or not. The POWER5 just broke the 3 million transactions per minute barrier on the TPC-C benchmark."
Where's the bit on the true origins of AI?
dW: That is a shame. I have one more on the subject of OSes -- was AIX really designed by space aliens?
McCalpin: I hadn't heard that one. It feels like it was designed by, [not space aliens, but] in some part by people with mainframe backgrounds..."
Apparently the aliens have embedded mind control in AIX!
I stopped reading the article after I saw this:
That's my classification, but we don't have any other kinds of titles here. On my office door the sign says, "Dr. Bandwidth" - is that a title?
I wonder if ignorant people actually address him as such?
I worked recently as a contractor for IBM where I helped contribute to the design decisions for the POWER7. This article is great because it describes how the design decisions happen at IBM and it is right on the money. It's interesting because the way IBM does it is different from most other companies.
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A good quote to break out when people claim that cluster supercomputers are "better" than vector supercomputers (when they're really two different types of systems with differing strengths that can't be directly compared):
>McCalpin: The majority of high-end systems are used for throughput workloads of one kind or another. The vector machines, both from NEC and Cray(TM), are very well-liked by the end users because vectorization is a relatively easy thing to understand, how to write code that will vectorize. And the machines -- with relatively little effort -- give you a good utilization, you'll get a good fraction of the peak theoretical performance without a whole lot of work. And customers find that comforting. You put the code on there, you get 35% of the theoretical peak performance and you say, "Well, that's pretty good and I don't need to mess with it anymore."
On the machines that IBM sells and that HP sells and AMD(TM) and all of the others, the costs are much lower, but it's harder to get very high utilization on those machines, in part because they don't have so much expensive memory bandwidth. So there's an interesting discrepancy between the end users who love vector machines because they're easy to use and then the purchasing manager who doesn't like vector machines because they cost too much.
The IBM POWER line (including PPC) is the one and only true threat to Intel's dominance of the hardware market. Remember that AMD pays royalties to Intel for every chip it sells, which pretty much condemns them to permanent second-place competitor.
Once the PPC 970 (or some successor) starts shipping in commodity beige boxes, however, the entire marketplace will be turned upside down. Can you imagine buying the generic equivalent of a dual proc G5 for $600? Sweet.
This interview was absolutely fascinating. The comment I found most interesting was McAlpin's opinion that 128-bit processing won't be coming to PC's any time soon. Excellent choice...
"Lack of technical competence coupled with the arrogance of power, as usual, leads to no good end."
Its just like 64 bit processing. What does it buy you? In 99.999% of the cases it means more crud to move around and less effecent use of memory. Going from 32 bits to 64 bits didn't buy as much as going from 16 to 32 did and going 64 to 128 is almost pointless. Now a 32 bit machine that can munch on 1024 bit data at a time in an effecent way would be useful but now they call that a "video card"
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You are right; I have thought about building a machine based around one of these ATI or Nvidia cards. It would be interesting to see if anyone has done this.
It's better & cheaper than the complex Itanium2's out-of-order-execution.
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