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0 pointsAardwolf1y ago0 comments

> There is no difference between Intel and AMD Zen 4 for most 512-bit AVX-512 instructions.

Except for the fact that Intel hasn't had any AVX-512 for years already in consumer CPUs, so there's nothing to compare against really in this target market

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adrian_b1y ago

The comparison done by the AMD announcement and by everyone else compares the Zen 5 cores, which will be used both in their laptop/desktop products and in their Turin server CPUs, with the Intel Emerald Rapids and the future Granite Rapids server CPUs.

As you say, Intel has abandoned the use of the full AVX-512 instruction set in their laptop/desktop products and in some of their server products.

At the end of 2025, Intel is expected to introduce laptop/desktop CPUs that will implement a 256-bit subset of the AVX-512 instruction set.

While that will bring many advantages of AVX-512 that are not related to register and instruction widths, it will lose the simplification of the high-performance programs that is possible in 512-bit AVX-512 due to the equality between register size and cache line size, so the consumer Intel CPUs will remain a worse target for the implementation of high-performance algorithms.

BeeOnRope1y ago

> of the high-performance programs that is possible in 512-bit AVX-512 due to the equality between register size and cache line size, so the consumer Intel CPUs will remain a worse target for the implementation of high-performance algorithms.

Can you elaborate here? I love full-width AVX-512 as much as the next SIMD nerd, but I rarely considered the alignment of the cache line and vector width one of the particularly useful features. If anything, it was a sign that AVX-512 was probably the end of the road for full-throughput full-width loads and stores at full AVX register width, since double-cache line memory operations are likely to be half-throughput at best and a doubling of the cache line width seems unlikely.

celrod1y ago

I read that comment as "the wider, the sweeter" (which I agree with), but that we're now (as you say) at the end of the road, and thus the sweetest point.

But an increase in cacheline size would be nice if it can get us larger vectors, or otherwise significantly improve memory bandwidth.

adgjlsfhk11y ago

it does seem plausible. Apple has gone to 128 bit cache line.

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