Amdahl's law, 55 years later

AVX-512 adds a large set of useful features that work at all vector lengths that expand its total applicable use cases. Some instructions are just more powerful, more general, with lower cost at fewer cycles. In existing code, using these new instructions can make some loops or fast paths much faster, think like 20% improved. And this is practically free performance because the silicon is there, the cost has already been paid for you; the expanded register file and ALU area is not the dominant cost of the die. Most of the complaints about Haswell-era AVX implementation defects like all-core throttling haven't been relevant since Ice Lake (google "intel cpu core power licensing"). Modern AMD systems don't have this issue either.

Amdahl's law doesn't really mean anything here, because the most basic way of applying it is measuring a _single_ enhancement versus the system baseline at a single point in time. But making these instructions more useful with more features, more widely applicable, and improving their speed, expands the number of cases where they can be applied beneficially. Thus, the overall proportion of the system where improvements are possible has increased. This fact is not captured by the basic application of the law.

The reality is that AVX-512 is extremely nice to use but Intel completely fucked up delivering it to client systems, from what I can tell, due to their weird dysfunction and total addiction to product segmentation. We could have already been long past worrying about it if not for that.