2 ms·
That was only on Skylake-X, which I admit was like 4 generations of Intel boxes. But its no longer true today. AMD's Zen4 doesn't downclock at all with AVX512
by dragontamer 3y ago
That was only on Skylake-X, which I admit was like 4 generations of Intel boxes.
But its no longer true today. AMD's Zen4 doesn't downclock at all with AVX512 instructions, and modern Intel chips have only like 100Mhz (aka 0.1Ghz) of downclock measured in practice.
In any case, AVX512 is certainly a win from a power-performance perspective. You get more compute-work done with far less decoding/other CPU-related internal core stuff. Even on Skylake-X, I'd expect that AVX512 sorting routines will heat up the CPU less than a non-AVX512 sorting routine... and otherwise be superior from a head and/or power limited perspective.
- comex 3y agoSounds like you’d still want a non-AVX512 path for sufficiently small arrays, though. As an extreme case, sorting a 4-element array presumably doesn’t get enough speedup from AVX512 to be worth downclocking by 100Mhz. I wonder where the cutoff is.
- dragontamer 3y agoThe 100MHz downclocking is only seen in Icelake, and not in Rocketlake (no perceptive downclocking behavior from any AVX512). So its a lot of effort to think about a problem that's only identified on a relatively small number of server processors, and (probably) won't be a problem moving forward.