On Thu, Sep 24, 2009 at 12:40 PM, Hearns, John <[email protected]> wrote: > Internal ring buses? How long till you lot are benchmarking them and > claiming your > code is taking too long because the data is moving round the bus in the > wrong direction :-)
Well, if you add cache coloring (http://en.wikipedia.org/wiki/Cache_coloring) to the mix, you can pretty much have the whole DC metro running in you cores. :) > I thought understanding L1, 2 and 3 caches was hard enough, without > having to think about rings. Since creating a monolithic 24MB L3 cache would have make it slow as a slug, they basically added a second level of L2 cache, local to each core, and connected them together with a bidirectionnal bus, so that "if any core needs a byte from any other cache, it is no more than 4 ring hops to the right cache slice." It looks a bit like HT Assist (http://www.bit-tech.net/news/hardware/2009/06/01/amd-launches-6-core-istanbul-opteron-proces/1)? Except it's in-chip rather than inter-CPUs. And it's supposed to behave like a large shared L3. > Ah well. Toroids on chip next? Further down, in the posted article: "The transistor count of 2.3 billion backs that up. To make it all work, the center of the chip has a block called the router. It is a crossbar switch that connects all internal and external channels, up to eight at a time." The chip itself is becoming a NUMA-like system, with its own internal network, a crossbar switch and its own internal topology. At some time, if the number of cores continues to grow, it wouldn't be that surprising to see some locality emerge, in the form of local clusters of cores, tightly coupled on a bus ring, and interconnected to other cluster of cores through QPI links (intra- or inter-chips). Network architectures as we see them today at the Infiniband interconnect level could very well make their way into the chips. So yes, toroids, why not? :) "With 4 QPI links, 8 memory channels, 8 cores, 8 cache slices, 2 memory controllers, 2 cache agents, 2 home agents and a pony, this chip is getting quite complex." You bet! Cheers, -- Kilian _______________________________________________ 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
