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Comment by kllrnohj | Hacker News Reader

I think you're either underestimating how much power an A12 consumes or overestimating what actively cooled CPUs consume per-core.

The A12 will pull around 4w on a single-core workload to come close to 9900K in performance. That's a good number, but it's not unheard of. The 4800HS is also a 4w per core CPU, and also comes close to the 9900K in performance.

The problem is increasing single-core performance becomes non-linear. It's not just a few more watts to bump from 3ghz to 4ghz. It's a lot of watts.

Simply having 4 big cores on an A12 would push it into 10w actively cooled territory as well, same as the i5 in a macbook air (a CPU that's also 10w). Add a few watts to bump the single core performance while you're at it and suddenly it's a 20w chip. Make it 8-cores to compete with the current macbook pro CPUs and suddenly it's a 40w chip.

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> "Simply having 4 big cores on an A12 would push it into 10w actively cooled territory as well"

The A12X/A12Z already has 4 big cores (and 4 little cores, and 7-8 GPU cores). I imagine the A14X will follow this pattern, but the cores will be 2 generations newer, with 2 generations of performance-per-watt improvements.

Rumors indicate all high-power cores.

Heterogenous cores are a pretty huge advantage.

Power-performance is a very nonlinear curve, so it doesn't make sense to compare single-core TDPs with all-core TDPs. The iPhone XS is 2500 MHz when one core, but drops to 2380 MHz when both primary cores are in use, a 5% performance drop... but this drop lowers power from 3.85 W to 2.12 W, 45% less!

Hence it makes much more sense to treat the A series processors as 2 watt chips when looking at multi-core scores. They're targeting efficiently hitting these lower frequencies. You'll get a similar result for the 4800HS; it'll use a lot more than 4 W single-core.

I think you mean 2w cores not 2w chips? The A12X also cuts frequency when multiple are in use (as of course AMD and Intel CPUs do as well), but at 2w/core you're still talking 8w for a quad core, comparable in power to the quad core i5 in the current MacBook Air.

The problem here is a severe lack of quality data. The best we have right now is SPEC2006 which is unfortunately only single core. You're absolutely right that it makes more sense to compare like for like in workloads, but we don't have any good multithreaded cross-platform benchmarks. There's geekbench, but it's somewhere between mediocre and shitty. And then nothing else? There's then no multithreaded benchmarks that also have measured power draw on an A12/A13.

A 4800HS at it's 4w/core all core load is also still clocking higher than an A12X. When Apple has the thermal budget to spend as well they'd almost certainly do the same thing?

Yes, 2 W/core. The difference is that at this power level, the A series chip will be a lot closer to peak performance than the Intel chip.

> A 4800HS at it's 4w/core all core load is also still clocking higher than an A12X.

This doesn't mean that much, since the range of efficient clock speeds depends on design choices, so they aren't always 1:1 comparable between architectures. Apple might well increase clock speed on their desktop chips, but unless it's only a few percent, it won't be as simple as pumping more power into the same dies; they have to actually redesign the core to operate efficiently at those higher speeds.

The A12 draws 4W when all four big cores are maxed out. Not 4W per big core. That's 4x the performance per watt of your comparable Intel or AMD parts.

No, it pulls 4W under the single-threaded spec2006. And the A13 then actually regresses on perf/watt and hits 6W in a few tests https://www.anandtech.com/show/14892/the-apple-iphone-11-pro...

This isn't unique to Apple, either. The "big" cores in ARM CPUs have been pulling 2-4W for years and years. That's why thermal throttling is such a major issue in mobile, especially mobile games.

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