Linus Torvalds: "I Hope AVX512 Dies A Painful Death"
Written by Michael Larabel in Intel on 11 July 2020 at 08:39 PM EDT. 115 Comments
INTEL --
Linux creator Linus Torvalds had some choice words today on Advanced Vector Extensions 512 (AVX-512) found on select Intel processors.

In a mailing list discussion stemming from the Phoronix article this week on the compiler instructions Intel is enabling for Alder Lake (and Sapphire Rapids), Linus Torvalds chimed in. The Alder Lake instructions being flipped on in GCC right now make no mention of AVX-512 but only AVX2 and others, likely due to Intel pursuing the subset supported by both the small and large cores in this new hybrid design being pursued.

The lack of seeing AVX512 for Alder Lake led Torvalds to comment:
I hope AVX512 dies a painful death, and that Intel starts fixing real problems instead of trying to create magic instructions to then create benchmarks that they can look good on.

I hope Intel gets back to basics: gets their process working again, and concentrate more on regular code that isn't HPC or some other pointless special case.

I've said this before, and I'll say it again: in the heyday of x86, when Intel was laughing all the way to the bank and killing all their competition, absolutely everybody else did better than Intel on FP loads. Intel's FP performance sucked (relatively speaking), and it matter not one iota.

Because absolutely nobody cares outside of benchmarks.

The same is largely true of AVX512 now - and in the future. Yes, you can find things that care. No, those things don't sell machines in the big picture.

And AVX512 has real downsides. I'd much rather see that transistor budget used on other things that are much more relevant. Even if it's still FP math (in the GPU, rather than AVX512). Or just give me more cores (with good single-thread performance, but without the garbage like AVX512) like AMD did.

I want my power limits to be reached with regular integer code, not with some AVX512 power virus that takes away top frequency (because people ended up using it for memcpy!) and takes away cores (because those useless garbage units take up space).

Yes, yes, I'm biased. I absolutely destest FP benchmarks, and I realize other people care deeply. I just think AVX512 is exactly the wrong thing to do. It's a pet peeve of mine. It's a prime example of something Intel has done wrong, partly by just increasing the fragmentation of the market.

Stop with the special-case garbage, and make all the core common stuff that everybody cares about run as well as you humanly can. Then do a FPU that is barely good enough on the side, and people will be happy. AVX2 is much more than enough.

Yeah, I'm grumpy.

Linus

While Alder Lake might not have AVX-512, the Xeon Sapphire Rapids still does and there are no indications Intel is planning to abandon AVX-512 on the Intel Xeon front with only building upon it with DL-BOOST and other extensions.

These words from Linus come just weeks after he switched to AMD Ryzen Threadripper for his primary development rig.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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