Hacker News Reader

Much better to burn the area for multiple smaller units, its a bit more area for frontend handling, but worth it for the flexibility (see Apple's M-series chips vs intel avx*).

View on HN

Yes and no. I think neon is undersized for today at 128bit registers -- if you're working with doubles for example, that's only two values per register, which is pretty anemic. Things like shuffles and other tricky bitops benefit from wider widths as well (see my other reply)

Agreed that 128 bit is undersized, but 512 feels pretty good for the time being. We're unlikely to see further size increases since going to 1024 would require doubling the cache line, register file, and ram bandwidth, while just adding an extra fma port is far less hardware.

totally - especially given how bandwidth constrained CPUs still are, going wider than 512 doesn't make much sense. 512 itself was a stretch for quite a long time (and all the negative press on the original implementations was a consequence of being not-quite-ready for primetime), but for current hardware I think it's perfect.

But 128bit is just ancient. If you're going to go to significant trouble to rewrite your code in SIMD, you want to at least get a decent perf return on investment!

128 bit is already really nice for things like Int8 comparison (e.g lots of string operations and Swiss Dict key search)

Reply on news.ycombinator.com