4 ms·

It costs a lot of area for something that's doesn't move the needle for the majority of desktop applications (browsers, games, office apps). The AVX512 units on

It costs a lot of area for something that's doesn't move the needle for the majority of desktop applications (browsers, games, office apps). The AVX512 units on Skylake-SP for example are a substantial portion of the area of each core. At some point you have to consider how many cores you could fit in the area used for vector extensions and make a trade-off.

aseipp 5y ago
This argument IMO is rather overblown. A quick die shot of Skylake-X indicates to me that even if you completely nerfed every AVX-512 unit appropriately (including the register files) on say, an 8-core or 10-core processor, you're going to get what? 1 or 2 more cores at maximum?[1] People make it sound like 70% of every Skylake-X die just sits there and you could have 50x more cores, when it's not that simple. You can delete tons of features from a modern microprocessor to save space but that isn't always the best way forward. In any case, I think this whole argument really misses another important thing, which is that the ISA and the vector width are separate here different. If Intel would just give us AVX-512 with 256b or 128b vectors, it would lead to a very big increase in use IMO, without having to have massive register files and vector data paths complicate things. The instruction set improvements are good enough to justify this IMO. (Alder Lake makes it a more complex case since they'd need to do a lot of work to unify Gracemont/Golden Cove before they could even think about that, but I still think it would be great.) They could even just half the width of the vector load/store units relative to the vector size like AMD did with Zen 2 (e.g. 256b vecs are split into 2x128b ops.) I'll still take it [1] https://twitter.com/GPUsAreMagic/status/1256866465577394181/photo/2 https://twitter.com/GPUsAreMagic/status/1256866465577394181/...
- gpderetta 5y ago
  Exactly. Even just one AVX512 ALU instead of the typical two would be an option (which in fact Intel has used on some *lake variants).
Aardwolf 5y ago
> It costs a lot of area for something that's doesn't move the needle for the majority of desktop applications But that could be a bit of a chicken and egg situation, right?
- paulmd 5y ago
  Absolutely. It's useful in text processing, it's useful in emulation, it's useful for doing bit-math for various encodings and checksumming, etc. The newer revisions don't have any downclocking either. https://old.reddit.com/r/emulation/comments/lzfpz5/what_are_the_implications_of_avx512_for_emulation/ https://old.reddit.com/r/emulation/comments/lzfpz5/what_are_... https://travisdowns.github.io/blog/2020/08/19/icl-avx512-freq.html https://travisdowns.github.io/blog/2020/08/19/icl-avx512-fre... People have made some incredibly broad assertions about the technology as a whole on the basis of a first-gen product that lingered on the market for far too long because of the 10nm woes. People also hang on Linus's words far, far too much. He's incredibly toxic and willing to opine about stuff he's been disconnected from for 20 years. Lisa Su is putting her money where her mouth is, AMD is making a billion-dollar bet on AVX-512 at a time when Intel has actually abandoned it in the consumer market entirely. Maybe she's doing it just for the server market, but that still means she thinks server-market customers are going to see an actual benefit on normal server tasks, such that it will be worth making every single customer pay more for a larger piece of silicon. It's not the kind of thing you do "just to win a couple HPC benchmarks". Sorry, I trust the person with the financial stake in this discussion a lot more than I trust Linus's spit-takes.
janwas 5y ago
Those are surprising claims. Browsers and their video/image codecs use SIMD. Other usages in office/productivity apps include Photoshop/Lightroom, video editing, compression, CAD.

aseipp 5y ago

This argument IMO is rather overblown. A quick die shot of Skylake-X indicates to me that even if you completely nerfed every AVX-512 unit appropriately (including the register files) on say, an 8-core or 10-core processor, you're going to get what? 1 or 2 more cores at maximum?[1] People make it sound like 70% of every Skylake-X die just sits there and you could have 50x more cores, when it's not that simple. You can delete tons of features from a modern microprocessor to save space but that isn't always the best way forward. In any case, I think this whole argument really misses another important thing, which is that the ISA and the vector width are separate here different. If Intel would just give us AVX-512 with 256b or 128b vectors, it would lead to a very big increase in use IMO, without having to have massive register files and vector data paths complicate things. The instruction set improvements are good enough to justify this IMO. (Alder Lake makes it a more complex case since they'd need to do a lot of work to unify Gracemont/Golden Cove before they could even think about that, but I still think it would be great.) They could even just half the width of the vector load/store units relative to the vector size like AMD did with Zen 2 (e.g. 256b vecs are split into 2x128b ops.) I'll still take it [1] https://twitter.com/GPUsAreMagic/status/1256866465577394181/photo/2 https://twitter.com/GPUsAreMagic/status/1256866465577394181/...

gpderetta 5y ago
Exactly. Even just one AVX512 ALU instead of the typical two would be an option (which in fact Intel has used on some *lake variants).

Aardwolf 5y ago

> It costs a lot of area for something that's doesn't move the needle for the majority of desktop applications But that could be a bit of a chicken and egg situation, right?

paulmd 5y ago
Absolutely. It's useful in text processing, it's useful in emulation, it's useful for doing bit-math for various encodings and checksumming, etc. The newer revisions don't have any downclocking either. https://old.reddit.com/r/emulation/comments/lzfpz5/what_are_the_implications_of_avx512_for_emulation/ https://old.reddit.com/r/emulation/comments/lzfpz5/what_are_... https://travisdowns.github.io/blog/2020/08/19/icl-avx512-freq.html https://travisdowns.github.io/blog/2020/08/19/icl-avx512-fre... People have made some incredibly broad assertions about the technology as a whole on the basis of a first-gen product that lingered on the market for far too long because of the 10nm woes. People also hang on Linus's words far, far too much. He's incredibly toxic and willing to opine about stuff he's been disconnected from for 20 years. Lisa Su is putting her money where her mouth is, AMD is making a billion-dollar bet on AVX-512 at a time when Intel has actually abandoned it in the consumer market entirely. Maybe she's doing it just for the server market, but that still means she thinks server-market customers are going to see an actual benefit on normal server tasks, such that it will be worth making every single customer pay more for a larger piece of silicon. It's not the kind of thing you do "just to win a couple HPC benchmarks". Sorry, I trust the person with the financial stake in this discussion a lot more than I trust Linus's spit-takes.

janwas 5y ago

Those are surprising claims. Browsers and their video/image codecs use SIMD. Other usages in office/productivity apps include Photoshop/Lightroom, video editing, compression, CAD.