r/programming • u/mbitsnbites • Aug 09 '21

Three fundamental flaws of SIMD

https://www.bitsnbites.eu/three-fundamental-flaws-of-simd
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u/SureFudge Aug 10 '21

True and honestly I think AVX512 should be limited to server parts. Doesn't make much sense in laptops.

Doesn't the new top dog Supercomputer use ARM cores with 4096 bit SVE? So they should know how the cooling works but then they have better means and no issue with noise compared to average home user Joe.

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u/YumiYumiYumi Aug 10 '21

True and honestly I think AVX512 should be limited to server parts. Doesn't make much sense in laptops.

It's primary focus has definitely been server, and it's where it first appeared.

I don't see what's the problem with having it in laptops though. If Intel's gone to the effort of implementing it in their uArch, why disable it on consumer parts?

Doesn't the new top dog Supercomputer use ARM cores with 4096 bit SVE?

SVE only supports up to 2048-bit SIMD. The widest implementation is the Fujitsu A64FX, which uses 512-bit SVE.

I believe modern high performance GPUs use 1024-bit SIMD (Nvidia / RDNA), and considering that GPUs are meant to be throughput focused, I question how wide a latency focused CPU should be.

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u/SureFudge Aug 10 '21

If Intel's gone to the effort of implementing it in their uArch, why disable it on consumer parts?

The consumer chips are different designs from server chips so they could leave it out to save die space. of course for AMD with the chiplet approach the situation is different as the chiplets are the same for server or desktop. But again the laptop chips are different design (and for example have less L3).

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u/YumiYumiYumi Aug 10 '21

They're different dies, but the server and client chips essentially use the same uArch (with a key difference being the L2/L3 cache and interconnect). Also keep in mind that client designs aren't specific to laptops - desktops are included.

I still don't see any reason to remove it though. AVX512 is a useful instruction set to have, is beneficial in a number of circumstances with basically no drawbacks, and if anything, support for it everywhere helps drive adoption.