Anon (no.delete@this.spam.com) on June 2, 2022 12:35 am wrote:

> Apple is using TSMC 5nm while Intel is using 10nm which they call 7nm
> and AMD uses TSMC's 7nm, and both Intel Intel and AMD supports SMT.
>
> So, yes, Apple achieve almost the same performance at much lower power, but because they have power
> advantage and Intel and AMD are willing to use A LOT of extra power to get 20% single thread.
>
> Zen 4 will be more apples-to-Apple comparison, at least on throughput, where perf per watt is what matters.

That is the reply often given but I don't find it convincing. A14/M1 is not the only product at 5nm and yet it's peak performance and perf/watt so far are unmatched. Notebookcheck recently did a series of benchmarks comparing the efficiency and performance of latest CPUs at locked TDP, and a 5nm Firestorm at 4W outperformed a Zen 3+ at 9.5W — that's more than 2x difference in efficiency, and this is in a benchmark that maximally favours x86 as it runs a suboptimal code path on M1. I have hard time believing that TSMC's 5nm has some kind of magical properties that allows a vendor to reduce the power consumption by 2x at the same performance level.

Your other argument — that x86 vendors trade some of the inherent efficiency to get this extra 20% performance has more merit IMO, but still doesn't provide a satisfactory explanation. First of all, AMD Zen3 isn't any faster than Firestorm, except maybe in a handful of AVX2 SIMD throughput tests where it's higher clock lets it pull ahead. Intel is a bit different, since they generally seem fine with making power-hungry cores if they can get ahead in performance (in the test linked above Golden Cove is 20% faster than Firestorm — with a whopping 6x higher power consumption!). But to offset this, Intel is now adding throughtput/efficiency cores, which do exactly what you are talking about — trade peak performance for much lower power usage. And yet, when you compare Alder Lake E-cores to the P-cores, the former are around 40% slower at roundly 2.5x lower power consumption (SPEC2017, Anandtech). In contrast, Apple's Firestorm is around 10-15% slower than Golden Cove at average 5x lower power consumption. I mean, there is a gap between Intel's 10nm and TSMC's 5nm, but it just isn't that much of a gap. If it were just "Apple trades peak performance for better efficiency", I'd expect them to be 20-30% slower with 2-3x lower power consumption, but they somehow do significantly better than that.

I will be also very curious to see how Zen4 performs in comparison. Given the less than perfect information we have available, it is really difficult to ascertain how much influence can be attributed to the process, to the ISA, to the design philosophy or maybe just the elusive "magic sauce" that individual vendors bring to the table.