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AVX2 is slower than SSE2-4.x under Windows ARM emulation

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Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#11

Post by kbolino »

jsheard wrote: post #8
kbolino wrote: post #5

I suspected this was because the vector units were not wide enough, and it seems that is the case. AVX2 is 256-bit, ARM NEON is only 128-bit. The big question then is, why are ARM desktop (and server?) cores so far behind on wider SIMD support? It's not like Intel/AMD came up with these extensions for x86 yesterday; AVX2 is over 15 years old.

SVE was supposed to be the next step for ARM SIMD, but they went all-in on runtime variable width vectors and that paradigm is still really struggling to get any traction on the software side. RISC-V did the same thing with RVV, for better or worse.

Yeah, the extensions exist, and as pointed out by a sibling comment to yours, have been implemented in supercomputer cores made by Fujitsu. However, as far as I know, neither Apple nor Qualcomm have made any desktop cores with SVE support. So the biggest reason there's no desktop software for it is because there's no hardware support.

Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#12

Post by jorvi »

SecretDreams wrote: post #3
iberator wrote: post #2

AVX2 should be banned anyway. Only expensive CPUs have it, ruining mininum games requirements and making hardware obsolete. Most of the world lives of 300$ per month

Almost every x86 cpu made in the last decade should have avx2. Maybe you're thinking of avx512 or avx10?

Yeah, sounds like they're confusing AVX2 for AVX512. AVX2 has been common for a decade at least and greatly accelerates performance.

AVX512 is so kludgy that it usually leads to a detriment in performance due to the extreme power requirements triggering thermal throttling.

Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#13

Post by jovial_cavalier »

leeter wrote: post #10
kbolino wrote: post #5

I suspected this was because the vector units were not wide enough, and it seems that is the case. AVX2 is 256-bit, ARM NEON is only 128-bit. The big question then is, why are ARM desktop (and server?) cores so far behind on wider SIMD support? It's not like Intel/AMD came up with these extensions for x86 yesterday; AVX2 is over 15 years old.

[removed]

A ton of vector math applications these days are high dimensional vector spaces. A good example of that for arm would I guess be something like fingerprint or face id.

Also, it doesn't just speed up vector math. Compilers these days with knowledge of these extensions can auto-vectorize your code, so it has the potential to speed up every for-loop you write.

Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#14

Post by badgersnake »

jorvi wrote: post #12
SecretDreams wrote: post #3

Earlier quoted context omitted.

Almost every x86 cpu made in the last decade should have avx2. Maybe you're thinking of avx512 or avx10?

Yeah, sounds like they're confusing AVX2 for AVX512. AVX2 has been common for a decade at least and greatly accelerates performance. AVX512 is so kludgy that it usually leads to a detriment in performance due to the extreme power requirements triggering thermal throttling.

I think that's slightly old information as well, AVX512 works well on Zen5.

Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#15

Post by SecretDreams »

jorvi wrote: post #12
SecretDreams wrote: post #3

Earlier quoted context omitted.

Almost every x86 cpu made in the last decade should have avx2. Maybe you're thinking of avx512 or avx10?

Yeah, sounds like they're confusing AVX2 for AVX512. AVX2 has been common for a decade at least and greatly accelerates performance. AVX512 is so kludgy that it usually leads to a detriment in performance due to the extreme power requirements triggering thermal throttling.

Agree. It's only recently with modern architectures in the server space that avx512 has shown some benefit. But avx2 is legit and has been for a long time.

Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#16

Post by Tuldok »

jsheard wrote: post #8
kbolino wrote: post #5

I suspected this was because the vector units were not wide enough, and it seems that is the case. AVX2 is 256-bit, ARM NEON is only 128-bit. The big question then is, why are ARM desktop (and server?) cores so far behind on wider SIMD support? It's not like Intel/AMD came up with these extensions for x86 yesterday; AVX2 is over 15 years old.

SVE was supposed to be the next step for ARM SIMD, but they went all-in on runtime variable width vectors and that paradigm is still really struggling to get any traction on the software side. RISC-V did the same thing with RVV, for better or worse.

The only time I've encountered ARM SVE being used in the wild is in the FEX x86 emulator (https://fex-emu.com/FEX-2407/).

Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#17

Post by kimixa »

jorvi wrote: post #12
SecretDreams wrote: post #3

Earlier quoted context omitted.

Almost every x86 cpu made in the last decade should have avx2. Maybe you're thinking of avx512 or avx10?

Yeah, sounds like they're confusing AVX2 for AVX512. AVX2 has been common for a decade at least and greatly accelerates performance. AVX512 is so kludgy that it usually leads to a detriment in performance due to the extreme power requirements triggering thermal throttling.

AMD's implementation very much doesn't have that issue - it throttles slightly, maybe, but it's still a net benefit. The problem with Intel's implementation is that the throttling was immediate - and took noticeable time to then settle and actually start processing again - from any avx512 instruction, so the "occasional" avx512 instruction (in autovectorized code, or something like the occasional optimized memcpy or similar) was a net negative in performance. This meant that it only benefitted large chunks of avx512-heavy code, so this switching penalty was overcome.

But there's plenty in avx512 the really helps real algorithms outside the 512-wide registers - I think it would be perceived very differently if it was initially the new instructions on the same 256-wide registers - ie avx10 - in the first place, then extended to 512 as the transistor/power budgets allowed. AVX512 was just tying too many things together too early than "incremental extensions".

Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#18

Post by jsheard »

kbolino wrote: post #11
jsheard wrote: post #8

Earlier quoted context omitted.

SVE was supposed to be the next step for ARM SIMD, but they went all-in on runtime variable width vectors and that paradigm is still really struggling to get any traction on the software side. RISC-V did the same thing with RVV, for better or worse.

Yeah, the extensions exist , and as pointed out by a sibling comment to yours, have been implemented in supercomputer cores made by Fujitsu. However, as far as I know, neither Apple nor Qualcomm have made any desktop cores with SVE support. So the biggest reason there's no desktop software for it is because there's no hardware support.

ARMs Neoverse IP does support SVE, so it's at least already relevant in cloud applications. Apparently AWS Graviton3 had 256bit SVE, but Graviton4 regressed back to 128bit SVE for some reason?

https://ashvardanian.com/posts/aws-graviton-checksums-on-neo...

Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#19

Post by bhouston »

kbolino wrote: post #5

I suspected this was because the vector units were not wide enough, and it seems that is the case. AVX2 is 256-bit, ARM NEON is only 128-bit. The big question then is, why are ARM desktop (and server?) cores so far behind on wider SIMD support? It's not like Intel/AMD came up with these extensions for x86 yesterday; AVX2 is over 15 years old.

Hasn't there been issues with AVX2 causing such a heavy load on the CPU that frequency scaling would kick in a lot of cases slowing down the whole CPU?

https://en.wikipedia.org/wiki/Advanced_Vector_Extensions#Dow...

My experience is that trying to get benefits from the vector extensions is incredibly hard and the use cases are very narrow. Having them in a standard BLAS implementation, sure, but outside of that I think they are not worth the effort.

Re: AVX2 is slower than SSE2-4.x under Windows ARM emulation

#20

Post by jsheard »

bhouston wrote: post #19
kbolino wrote: post #5

I suspected this was because the vector units were not wide enough, and it seems that is the case. AVX2 is 256-bit, ARM NEON is only 128-bit. The big question then is, why are ARM desktop (and server?) cores so far behind on wider SIMD support? It's not like Intel/AMD came up with these extensions for x86 yesterday; AVX2 is over 15 years old.

Hasn't there been issues with AVX2 causing such a heavy load on the CPU that frequency scaling would kick in a lot of cases slowing down the whole CPU? https://en.wikipedia.org/wiki/Advanced_Vector_Extensions#Dow... My experience is that trying to get benefits from the vector extensions is incredibly hard and the use cases are very narrow. Having them in a standard BLAS implementation, sure, but outside of that I thi…

Throttling was mainly an issue with AVX512, which is twice the width of AVX2, and only really on the early Skylake (2015) implementation. From your own source Ice Lake (2019) barely flinches and Rocket Lake (2021) doesn't proactively downclock at all. AMDs implementation came later but was solid right out of the gate.
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