Re:AVX-512, what’s useful for us
by justincormack on Friday December 22, 2017 @01:24PM
(#15989653)
They only cause slowdown on some models, if you pay Intel enough they wont. The advantage of AVX512 is you can use it on every core (rather than trying to work out how to partition a GPU), and it is useful for lots of general purpose computations.
[ Parent
| on HN ]
Re:AVX-512, what’s useful for us
by Dylan16807 on Friday December 22, 2017 @01:27PM
(#15989682)
What models don't slow down? Are you claiming the slowdown isn't actually necessary to keep the chip stable?
Re:AVX-512, what’s useful for us
by justincormack on Friday December 22, 2017 @03:28PM
(#15990633)
compare these
https://en.wikichip.org/wiki/intel/xeon_silver/4116#Frequenc...
https://en.wikichip.org/wiki/intel/xeon_gold/6154#Frequencie...
https://en.wikichip.org/wiki/intel/xeon_platinum/8180m#Frequ...
So platinum can run avx512 on 28 cores at 2.3GHz, while silver runs 12 cores at 1.4GHz
From your links, gold/plat has a ~15% clock speed hit when using ymm muls, then another ~20% hit when going to zmm muls.
So for 512-bit wide to not slow things down on Intel's chips, you need ~30% runtime of all cores to already be in AVX.
Xeon Phi, maybe? Since the entire raison d'être of that chip is doing avx-512 computation. Or if you're a glass half empty kind of person, you'd argue that it doesn't speed up when running scalar code. :)