AVX-512

Posted Oct 3, 2022 15:15 UTC (Mon) by drago01 (subscriber, #50715)
In reply to: AVX-512 by farnz
Parent article: Hybrid scheduling gets more complicated

Well there is also no downclock on Zen4.
But give how CPUs work now days that's not entirely true either because a lighter workload will result into higher clocks and vise versa. CPUs try to maximize performance within the power budget.

Clocks don't matter much though, what matters is the performance you are getting. And if you workload benefits from wide vectors it will offset any clock changes.

AVX-512

Posted Oct 3, 2022 15:33 UTC (Mon) by farnz (subscriber, #17727) [Link]

The critical difference is that with SKX, the maximum permitted clock assuming that thermals allowed was massively reduced for "heavy" AVX-512, because it caused thermal hot-spots on the chip that weren't properly accounted for by "normal" thermal monitoring. With ICL and with RKL there's no longer a huge limit - instead of the SKX thing (where a chip could drop from 3.0 GHz "base" to 2.8 GHz "max turbo" if you used AVX-512), you now can always sustain the same "base", but the max turbo is reduced by 100 MHz or so.

AVX-512

Posted Oct 13, 2022 13:54 UTC (Thu) by roblucid (guest, #48964) [Link]

Dr Ian Cutress tested various AVX usages on Zen4 and both power and performance benefited with AVX512 with an exception that lost about 5%. He was impressed with the lack of downsides.