Re:Are Experts Real?
by vlovich123 on Tuesday January 12, 2021 @01:08PM
(#25750803)
Nowhere did Linus say that AVX512 being a power sink is an unavoidable consequence and should be dropped for that reason. He just said "AVX512 sucks right now - they should spend their resources elsewhere because the ROI isn't there". When he made that statement he was factually correct - Intel had spent a lot of resources bringing AVX512 to market, the first version is shit (making correct selection of turning on AVX512 support tricky), & they had to spend even more correcting it.
If you had said 10 years ago "ARM sucks because it's in order" you wouldn't be factually wrong on that front in that in-order sucks for performance, but you would be factually wrong because the first iPhone was already partially out-of-order and 10 years ago you'd be looking at the iPhone 4 which was a Cortex-A8 superscalar design. Also in-order is fantastic for battery - that's why M4 & below are still in-order. Note that me saying this doesn't imply that will remain the case for all time, which is how you seem to be interpreting statements like that which would be an extremely poor interpretation on the part of the reader.
If I, 5-years or 10-years ago, claimed ARM sucks because its in-order, then I'd be making a similar mistake as Linus did. There's nothing about the ARM-ISA that forced in-order execution, it was just the norm (because back then: it was considered more power-efficient to make in-order chips).
There's nothing part of AVX512 that says "You must use more power than other instructions". That was just how it was implemented in Skylake-X. And lo-and-behold, one microarchitecture later, the power-issue is solved and a non-issue.
Similarly, ARM chips over the past decade switched to out-of-order style for higher performance. Anyone who was claiming that ARM was innately in-order would have been proven wrong.
----------
Maybe it takes experience to see the ebbs and flows of the processor world. But... that's what I'd expect an "expert" to be. Someone who can kind of look forward through that.
I mean, I've watched NVidia GPUs go superscalar (executing INT + FP simultaneously). I've watched ARM go from largely in-order microcontrollers into out-of-order laptop-class processors. I've watched instruction sets come and go with the winds.
------
If that's not good enough for you, then remember that Centaur implemented AVX512 WITHOUT power-scaling issues back in 2019, still predating Linus's rant by months. A chip did exist without AVX512 power throttling, and he still ranted in that manner.