5 ms·

What's the topology of these machines? Dual socket 64c chips with some reserved (or disabled)?

• wmf 7y ago
  They don't say that but that's the only way to provide 224 threads.
  • lallysingh 7y ago
    Darnit, I was hoping I was wrong and we were getting a hint of some new beast with 112 cores...
  • bob1029 7y ago
    Their topology tells far richer tales than the press releases when you dig deeper on the numbers. 224 threads = 112 HT cores = 2 x 56 core CPUs. This is 8 cores short of the 64 core flagship. 8 cores == 1 CCX. It seems exceedingly unlikely that AMD would produce a Rome CPU with 7 out of 8 CCX in perfect health, but have the 8th CCX completely missing (functionally). It seems more likely that the 8th CCX is there with all 8 cores, and that it is reserved for some other type of service. One possibility could be that there are higher guarantees of side channel protection at the CCX boundary, and google intends to use this for secure internal functions or sell to clients who have side channel sensitivity. Another may be that they simply want the hypervisor to have a very fat budget of 8 cores per socket to work with. Considering the amount of potential IO going on, this might be required in some cases.
    • smueller1234 7y ago
      See also boulos' comment: "As for 224, we've always reserved threads on each host for I/O and so on. Figure 2 from the Snap paper [1] is probably the best public reference. We also don't make it clear (on purpose) what size the underlying host processors are, though you can clearly guesstimate pretty easily." Ie. if there's even one thread reserved on the host, your speculation comes to naught. Sorry.