> ...first generation of EPYC, ... attaching each one to two memory channels, resulting in a non-uniform memory architecutre (NUMA).
OK
> 2nd Gen EPYC, ... solved this. The CPU design implements a central I/O hub through which all communications off-chip occur.
Well it's solved in that all mem accesses now uniformly are a bit slower as all have to go through the new memory access hub. Is this a correct reading?
also
> The CCDs consist of two four-core Core CompleXes (1 CCD = 2 CCX). ... those CCX can only communicate with each other over the central I/O die. There is no inter-chiplet CCD communication.
What is the communication for, presumably the MESI (or whatever AMD uses) cache coherence stuff, and poss. the sync instructions (CAS, atomic increment) too? Anything else I'm missing?
Thanks
(edit: bloody love that you can click the 'Print This Article' button and it becomes a single long web page. Webbyness as god intended).
> Well it's solved in that all mem accesses now uniformly are a bit slower as all have to go through the new memory access hub. Is this a correct reading?
Yes. But the new EPYC chips have doubled their L3 cache, and that new memory-access hub has stupidly high bandwidth.
The larger L3 cache mitigates the latency problems, while the memory-access hub has more than enough memory-bandwidth to feed all the cores.
> ...first generation of EPYC, ... attaching each one to two memory channels, resulting in a non-uniform memory architecutre (NUMA).
OK
> 2nd Gen EPYC, ... solved this. The CPU design implements a central I/O hub through which all communications off-chip occur.
Well it's solved in that all mem accesses now uniformly are a bit slower as all have to go through the new memory access hub. Is this a correct reading?
also
> The CCDs consist of two four-core Core CompleXes (1 CCD = 2 CCX). ... those CCX can only communicate with each other over the central I/O die. There is no inter-chiplet CCD communication.
What is the communication for, presumably the MESI (or whatever AMD uses) cache coherence stuff, and poss. the sync instructions (CAS, atomic increment) too? Anything else I'm missing?
Thanks
(edit: bloody love that you can click the 'Print This Article' button and it becomes a single long web page. Webbyness as god intended).