Re:Arm Announces New Mobile Armv9 CPU Microarchitectures
by zsmi on Tuesday May 25, 2021 @04:27PM
(#27282156)
It's even harder than that.
SVE vs NEON performance will also hugely depend on the vector length the given algorithm requires, and the stress that the instructions put on the memory subsystem.
Memory hierarchy varies by product and will likely continue to do so regardless of what M2 does.
In the end, I echo eyesee's comment, for best performance one should really use Accelerate.framework on Apple's hardware.
Re:Arm Announces New Mobile Armv9 CPU Microarchitectures
by brokencode on Tuesday May 25, 2021 @06:02PM
(#27283300)
My point was that it probably doesn’t matter. M1 is already very fast, even without SVE. At some point you just have to decide to ship a product, even if it doesn’t have every possible feature.
Like other posters mentioned, for vector operations like this, you could be dynamically linking to a library that handles this for you in the best way for the hardware. Then when new instructions become available, you don't have to change any of your code to take advantage.
* only use NEON to save developer time and lose performance and forward compatibility
* only use SVE to save developer time and lose backward compatibility
* Pay to support both and deal with the cost/headaches
Experience shows that AVX took years to adopt (and still isn't used for everything) because SSE2 was "good enough" and the extra costs and loss of backward compatibility weren't worth it.
If SVE were supported out of the gate, then the problem would simply never exist. Don't forget (as stated before) that there's been a huge wave of M1 buyers. People upgraded early either to get the nice features or not be left behind as Apple drops support.
Let's say you have 100M Mac users and an average of 20M are buying new machines any given year (a new machine every 5 years). The 1.5-2-year M1 wave gets 60-70M upgraders in the surge. Now sales are going to decline for a while as the remaining people stick to their update schedule (or hold on to their x86 machines until they die). Now the M2 with SVE only gets 5-10M upgraders. Does it make sense to target such a small group or wait a few years? I suspect there will be a lot of waiting.