>> https://docs.google.com/file/d/0B83UyWf1s-CdZnFoS2RiU2lJbEU/edit?usp=drive_web > Interesting, but depressing, presentation.
I found it unilluminating, actually. don't we all know about power issues? to me it raised two interesting questions: - what software and hardware architecture would better optimize communication to address the flop/bps per-joule divergence? here's a bluesky/strawman: put all the migration/coherence stuff into hardware. imagine if all cpus were globally cache-coherent, and the objects being cached were not just cache lines, and could having their sharing/migration semantics defined by the program. you might be saying "oh, but caches are not energy-efficient compared to static resources like registers". well, let's JIT the local code to refer to the static local address of an item when cached, rather than relying on a CAM - after all, if hardware is managing the cache, it can rename all references in the instruction stream... - do we need exascale anyway? would the world be better off with a thousand petascale machines? I know the field tends to view this as a kind of manifest destiny, but why? the secondary argument usually devolves to something like "well, the high end pushes the envelope so the masses can benefit from trickle-down improvements." but if this is the main justification, it's a bit twisted: we need to make clusters so big that we can't afford to power them in order to force ourselves to develop more power-efficient systems? if power is an important TCO component, why aren't we optimizing for it already (in any sized facility)? > At HotInterconnects in 2011, Intel gave a presentation about the reductions > in power per flop over time. The corresponding communication power > consumption per bit was flat (no improvement). Projecting the trends well, it has to be said that most computation is mundane and doesn't require multiple processors, let alone big clusters. so the fact that the computer industry focuses on this domain is appropriate. > forward and with a 20 Mw power budget, an exascale machine's network would > consume all the power leaving nothing for computation. well, that sounds absurd - were they assuming a full-bisection fat tree of older (hotter, lower fanout) generation interconnect? _______________________________________________ Beowulf mailing list, [email protected] sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
