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Doesn’t AMD also provide hyper-threading of sorts? My Ryzen has 6 cores and 12 threads. Isn’t that pretty much the same?
by josteink 5y ago
Doesn’t AMD also provide hyper-threading of sorts?
My Ryzen has 6 cores and 12 threads. Isn’t that pretty much the same?
- altusbrown 5y agoSomething about the AMD implementation is notably harder to exploit, though last I looked it wasn't clear what that was. It's held up much better, and a lot of people have looked at it. Still exploits, but almost impossible to do in the field last I checked, where Intel has been demonstrated on live systems handling production load.
- to11mtm 5y agoIt's difficult to say why AMD's implementation has held up better. One interesting thing I noted looking at wikichip's info [0] was that Zen calls out that Cache is tagged by thread. I wonder whether Intel's HT did/does the same or not. [0] https://en.wikichip.org/wiki/amd/microarchitectures/zen#Simultaneous_MultiThreading_.28SMT.29 https://en.wikichip.org/wiki/amd/microarchitectures/zen#Simu...
- rwaksmunski 5y agoI heard somewhere that AMD speculated a bit less and cleaned up a little after a miss, which made exploitation a lot more difficult. I'm sorry I don't recall the source, might have been an interview with one of AMD's engineers.
- schlupa 5y agoThe fundamental difference is that AMD respects exclusion domains even when speculating a thing intel is notorious for not doing. It's a fundamental difference. Intel: speculate without checking rights and crush afterward if a violation happened. Gains some points in benchmarks but makes side channel exploits very interesting. AMD: speculate only on allow if allowed. No need to crush afterward, no speculation violate security. Costs some points in benchmarks but make side channel exploits not very interesting.
- sundvor 5y agoIt's simply SMT or Simultaneous multithreading on AMD. Hyperthreading was Intel's branding of SMT, if I understand this correctly. Mine has 12 and 24. :)
- sundvor 5y agoIt's simply SMT or Simultaneous multithreading on AMD. Hyper-Threading was Intel's branding of SMT, if I understand this correctly. My Ryzen has 12 and 24. Simply amazing what they did. :)
- sundvor 5y agoApologies for the dupe; this was the most recent version, I thought I hit edit to correct the capitalisation of HT, but I obviously didn't.