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Comment by josteink | Hacker News Reader

Doesn’t AMD also provide hyper-threading of sorts?

My Ryzen has 6 cores and 12 threads. Isn’t that pretty much the same?

Something 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.

It'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#Simu...

I 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.

The 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.

It'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. :)

It'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. :)

Apologies 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.

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