Earlier quoted context omitted.
It's not the memory model I'm thinking of but the cache design, ROB size etc. Obviously this is fairly niche but the friction to making something fast is hugely easier locally.
The vast majority of developers never profile their code. I think this is much less of an issue than anyone on HN would rank it. Only when the platform itself provides traces do they take it into consideration. And even then, I think most perf optimization is in a category of don't do the obviously slow thing, or the accidentally n^2 thing. I partially agree with you though, as the penetration of Arm goes deeper into…
Protip: New on the job and want to establish a reputation quickly? Find the most common path and fire a profiler at it as early as you can. The odds that there's some trivial win that will accelerate the code by huge amounts is fairly decent.
Another bit of evidence developers rarely profile their code is that I can tell my mental model of how expensive some server process will be to run and most other developer's mental models tend to differ by at least an order of magnitude. I've had multiple conversations about the services I provide and people asking me what my hardware is, expecting it to be run on some monster boxes or something when I tell them it's really just two t3.mediums, which mostly do nothing, and I only have two for redundancy. And it's not like I go profile crazy... I really just do some spot checks on hot-path code. By no means am I doing anything amazing. It's just... as you write more code, the odds that you accidentally write something that performs stupidly badly goes up steadily, even if you're trying not to.