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simple lemma about pipelines
The connection between group structure and pipeline design seems like it merits a lot more attention than it gets. It’s not too hard to show that in a pipeline like the one to the right, the induced monoid of M1 must be a homomorphic image of the composite state machine. This immediately brings in the…
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The Amory Lovins bottleneck
Lovins observes that power inputs in many industrial processes go into a bottleneck that makes power conservation hard if you start at the wrong end. The power goes into a long pipeline of process that emerges on the other end with some useful (in theory) work. If you start on the power input end, then…
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An interesting article in ACM communications: is the world ending?
Coverity has a program that reads other programs looking for errors. The company started as a research project from Stanford (how unusual!) and the Communications article is really about what they found in commercial world. One thing they found was a lot of crappy programmers. Upon seeing an error report saying the following loop body…
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Recursion and state update and Hungarian Mathematicians
Please see this ever modifying page which seeks to demonstrate in a poorly organized, yet humorous manner, what the hell I’m trying to accomplish with this primitive recursive state machine stuff. And as an added bonus – the great “Recursive Functions” book by Rozsa Peters contains the following remarkable note that has nothing to do…
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Instructions per joule – a good start
… multi-GHz superscalar quad-core processors can execute approximately 100 million instructions per Joule, assuming all cores are active and avoid stalls or mispredictions. Lower-frequency in-order CPUs, in contrast, can provide over 1 billion instructions per Joule—an order of magnitude more efficient while still running at 1/3rd the frequency. Worse yet, running fast processors below their…
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sequential and combinational state machines
There’s a correspondence between the notions of “combinational” and “sequential” in digital circuit engineering and some structure in state machines (and therefore monoids) that seems interesting. In digital logic, a “combinational” circuit like a logic gate has can be associated with a time T so that the output depends only on input signals applied over…
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Why Computer Science is a failed field #2
I mentioned the phobia against mere experimentation recently, but now I have some more fascinating glimpses into “peer review”. I have some theoretical work I’m trying to finish up and get published somewhere so someone smart can do something with it. It may be junk or not – that’s why we have “peer review” in…
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Linux descends into priority inheritance hell
The PI chain walk is implemented by the function rt_mutex_adjust_prio_chain. The implementation has gone through several iterations, and has ended up with what we believe is the best. It walks the PI chain by only grabbing at most two locks at a time, and is very efficient. The rt_mutex_adjust_prio_chain can be used either to boost…