On Mon, Apr 15, 2013 at 3:10 PM, Pascal J. Bourguignon < [email protected]> wrote:
> I think that one place where "light cone" considerations are involved is > with caches in multi-processor systems. If all processors could have instantaneous knowledge of what the views of the other processors are > about memory, there wouldn't be any cache coherence problem. But light > speed, or information transmission speed is not infinite, hence the > appearance of light cones or "light cones"-like phenomena. Many people seem to jump from one extremism to another - from "instantaneous transfer" to "unbounded delay" - without seriously considering the useful middle (predictable, bounded delay). The middle has many models (including cellular automata) and is capable of supporting synchronous/real-time distributed systems. It's also where you'll find light cones... and many interesting, efficient synchronization patterns. Interestingly, cache coherence is not a problem if your programming model *doesn't* assume instantaneous transfer, i.e. because you'd end up explicitly modeling the delays and thus managing the distinct views in a formal manner - using distinct locations in memory, and thus distinct cache lines. (I believe this contributes to the success of modeling multi-processor systems as distributed systems.) Regards, Dave
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