The instructions 3DNow! came to AMD as a multimedia extension for x86 and that improved Intel's MMX set, since they were SIMDs that could handle floating point data, in addition to integers. The K6-2 from 1998 was the first microprocessor where they debuted. And since then major operating systems have included support for them, including Linux.
When Intel created SSE, similar to 3D Now !, AMD's extensions gradually became less relevant, until finally AMD itself abandoned them and no longer incorporated them in its latest microarchitectures. Therefore, for a few years, the processors of this firm have already stopped using them (in the AMD FX Bulldoer of 2011) and the Linux kernel support it becomes more and more irrelevant.
Therefore, to keep a lighter Linux kernel and eliminate old hardware drivers and this type of code, now will be removed from Linux kernel 5.17. After 24 years, it is time that they gave way to another more current and necessary code. In fact, not only are these going to be removed, but some other reshuffles are going to be carried out to make the kernel work better.
Remove the support code for the 3D Now! Multimedia instruction set. AMD will eliminate nothing less than 500 lines of code They have been there for decades. They are not too many when compared to other much more monstrous parts, but it is a quite relevant "void".
Now we just have to wait for the final version of the Linux kernel 5.17 and see what other surprises it has, since it will not be the only thing that is modified for this version, far from it ... Corrections are expected, more drivers, optimizations of existing code, performance improvements in the network TCP stack, and much more.