Testing a Chinese x86 CPU: A Deep Dive into Zen-based Hygon Dhyana Processors

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• anarekist - Thursday, February 27, 2020 - link

  that was a great and detailed article, very much appreciated.

• Notmyusualid - Sunday, March 1, 2020 - link

  I very much enjoyed it also.

• PeterCordes - Thursday, February 27, 2020 - link

  RDRAND isn't just a PRNG, it's still supposed to be based on true randomness. https://en.wikipedia.org/wiki/RDRAND
  It being faster doesn't necessarily indicate lower quality. See https://crypto.stackexchange.com/questions/29894/a... for some hardware details on the circuit AMD uses to turn analogue noise into digital randomness. (Apparently sampling asynchronous ring oscillators, and feeding that through some digital mixing functions (e.g. a hash) to "whiten" the result. Intel's design is similar, but based on sampling thermal noise.)
  
  RDSEED is merely even higher-quality randomness, suitable for seeding a PRNG instead of using directly. (It does not, as you mis-state, seed RDRAND. It's just a differently-processed way of pulling data from the same true HW randomness). Also unlike Linux /dev/random, it doesn't collect randomness from "various sources" into an entropy pool; my understanding is that all the randomness comes from a true HW RNG.
  
  Perhaps they had to redesign (for export-control reasons) the digital mixing functions that "whiten" the hardware randomness? A much more conservative approach for RDSEED could easily explain it being much slower, like if they didn't want to trust AMD's design not to have NSA back-doors. Or simply a lower-effort or less skilled redesign by a 3rd party that wasn't part of the original design could account for it.
  
  AMD Zen had some RDRAND bugs (like always returning -1 in some conditions) that were fixed by microcode updates; perhaps Hygon fixed that in hardware instead of microcode if there was any problem that AMD used to need to work around?

• Duto - Thursday, February 27, 2020 - link

  Good job in calming the concerns of many, and we appreciate it. However, nothing can change the fact that valuable American technology was transferred to a foreign and potentially hostile power, who is led by a dictatorship that violates #humanrights on a daily basis, yes continental China. Equally problematic is the fact that for a few dollars, AMD shoots on its feet, no turning back on that. It is evident that such disgrace took place under a very weak administration at home, in the current administration watch that wouldn’t happen, ever. So glad they close the deal for good!

• sarafino - Thursday, February 27, 2020 - link

  "Equally problematic is the fact that for a few dollars, AMD shoots on its feet, no turning back on that."
  
  How exactly did they do that? They shared designs based on their older (outdated), slower Zen core. As you can plainly see in this review, Hygon's processors are not exact setting the world on fire in terms of performance. They're slower than 3 year old Zen 1 processors and significantly slower than any Zen 2, or soon, Zen 3 processors. You're making a mountain out of a mole hill.

• Oxford Guy - Friday, February 28, 2020 - link

  Perhaps, but also consider that some of the world's leading supercomputers were made with Piledriver CPUs.
  
  Journalists like Hruska never miss an opportunity to mock AMD for its "construction core" debacle but when they talk about the poor performance of the parts they never mention how many supercomputers used them successfully. Sometimes being cheap and adequate is enough, especially when paired with high-performance GPUs.

• 29a - Monday, March 2, 2020 - link

  There is one in the Top 500 and it's ranked 481.

• Retycint - Thursday, February 27, 2020 - link

  I wouldn't be so sure that the "transfer of American tech to a foreign hostile power" won't happen under the current administration, given that they seem to have a special affinity for the Russians

• s.yu - Sunday, March 1, 2020 - link

  >they seem to have a special affinity for the Russians
  Not "they", but "he".
  What exactly has he transferred to Russia that hasn't been stopped by congress?

• jospoortvliet - Monday, March 2, 2020 - link

  Pretty much Syria, for one... and if he wasn't dragging his feed on support for Ukraine perhaps it would be free of russian soldiers by now as well.
  
  I know, it isnt intellectual property hehe