Linus Torvalds on AVX512

Post by gnufx » Mon, Jul 13, 2020, 9:25 AM UTC

AnthonyMouse wrote: post #83

gridlockd wrote: post #81

Earlier quoted context omitted.

Bulldozer significantly outperformed Sandy Bridge on the workloads which it was designed to be good at, which is multi-threaded integer workloads, like compiling the Linux kernel. https://www.phoronix.com/scan.php?page=article&item=amd_fx81... https://www.phoronix.com/scan.php?page=article&item=amd_fx83... If Linus' attitude of "I'd rather have more cores" and "FP doesn't really matter" were representative of market…

Are we looking at the same benchmarks? In the first they're comparing an 8-core Bulldozer to Sandy Bridge with 4 cores and no hyperthreading and it's basically even, sometimes it wins by a small margin on the threaded ones. In the second the 3770K has 4 cores with hyperthreading and that makes it look even worse. If they were actually getting twice the integer performance per module as Intel was getting per core then…

Post by panpanna » Mon, Jul 13, 2020, 10:52 AM UTC

TinkersW wrote: post #105

panpanna wrote: post #75

Earlier quoted context omitted.

This discussion is about avx512, which has shown to have some issues compared to other solutions. Nobody is claiming FP is garbage or that we don't ever need SIMD. Regarding Linus: he is almost always right. He has had more hands-on experience than everyone in this thread combined. I trust his judgement, he has earned it by being consistently correct while his opposition has just complained and eventually failed to d…

He likely has ~zero hands on experience with SIMD or AVX512 as those aren't used in his precious kernel.

Post by nix23 » Mon, Jul 13, 2020, 1:06 PM UTC

gnufx wrote: post #110

nix23 wrote: post #54

Earlier quoted context omitted.

ARM/RiscV with many cores...that's what i wrote, if you don't need a gpu you don't need one, if you need SVE you integrate it or use a co-Processor :)

SVE isn't in a co-processor, I guess is the point. There's a lot more to Fugaku than SVE (whether or not you think that's a version of avx512), though. No DDR is suggestive.

Post by xxs » Mon, Jul 13, 2020, 6:29 PM UTC

zozbot234 wrote: post #38

ArnoVW wrote: post #33

Earlier quoted context omitted.

They exist today, but they were added after AVX. Every year we figure out how to cram more transistors on a cubic cm, and once the low hanging fruit was added and we knew how to add more transistors, we decided to start putting more and more specific functions. That is the point of Linus. He would have preferred to use that increase in transistor count for other things, like more cache.

More cache has diminishing returns, because cache wants to be as close as possible to the core logic. And modern CPU's are mostly cache anyway. Special-purpose blocks for common compute tasks are quite cheap.

Post by jasonzemos » Mon, Jul 13, 2020, 9:30 PM UTC