this post was submitted on 03 Aug 2024
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[–] [email protected] 12 points 3 months ago (1 children)

Both chips are 20w class cpus, but the AMD cpu is much faster.

Apple CPUs don't report wattage, so it's a bit tricky to measure actual power consumption, but I can't imagine the AMD cpu uses 50% more power under load.

The Apple CPU might score some wins for idle power consumption though, considering the optimizations in MacOS, and the focus on power consumption across the whole system design.

[–] [email protected] 2 points 3 months ago* (last edited 3 months ago) (1 children)

You can definitely get fairly accurate power draw readings from these chips in macOS, even with Apple's own debugging tools. If anything, it's harder (or at least more confusing) to get accurate readings for AMD chips (TDP != power draw).

Also, the TDP the manufacturer states in the spec sheet pretty much doesn't mean anything these days. These chips will be allowed to draw different amounts of power for different durations under different conditions. This is especially true for the AMD parts, as they run in a lot of different laptops with different power and cooling capabilities. But even for Apple's M chips there are different configurations: a MacBook Air only has passive cooling while the same chip in a MacBook Pro can have active cooling, which will impact maximum allowed (sustained) power draw and with that, performance.

You also link to CPU Monkey, a website I wouldn't use for anything but very rough estimates, because their seemingly random collection of benchmarks are likely just taken/stolen from somewhere else (I doubt they benchmarked every single CPU they list themselves) and it's unclear with what power limits and thermal constraints these benchmarks were run.

Even with all the data, it's still hard to make a 100 % accurate comparison. For example, the efficiency curves of these CPUs is likely quite a bit different. The M3 might achieve its highest performance/watt at 12 watts, while the Ryzen's best performance/watt might be at 15 watts (these numbers are just an example). So, do you compare at 12 or 15 watts then?

And yes, there absolutely can be situations where the AMD CPU draws 50% or even 100% (or more) more power under load, and depending on the configuration of the chip in a specific system, the opposite can be the case as well. This in itself doesn't tell you much about potential power efficiency though.

EDIT: Also, comparing the Ryzen 9 part with 12 cores to the smallest M2 doesn't make any sense. You'd much more likely compare it to the M2 Max which has 12 cores as well (and again, trying to match the TDP in the spec sheet doesn't make any sense, as especially for AMD, TDP isn't even close to actual power draw under load - PPT is at least a somewhat better number here).

I also get that you're trying to match the process node as closely as possible and TSMC N4 is "just" an improed variant of TSMC N5P, but it still differs. Also, the M2 was released two years earlier than AMD's AI 300 series, so you ignore two years of architecture improvements which happen regardless of the process node, just look at the (supposed) performance and efficiency improvements from desktop Zen 4 to Zen 5 on the same.

Maybe the new AMD chips are better in many ways even compared to more recent Apple chips, but the comparison you are trying to make is so deeply flawed on so many levels that it's completely useless and it doesn't prove anything whatsoever.

[–] [email protected] 2 points 3 months ago

I've taken those facts into account.

I haven't seen any benchmarks that include power usage for Apple CPUs.

AMD cpus are not like Intel CPUs, they don't use more than the TDP under load. https://www.phoronix.com/review/amd-ryzen-ai-9-hx-370/3

The difference between N5P and N4 isn't significant compared to architectural differences, and the fact that Apple's architecture is inferior is exactly my point. If the AMD 370 and the Apple M3 are neck and neck, despite Apple being an entire process node ahead (5nm vs 3nm), that shows that Apple's architecture is inferior.

I don't think it's a fair comparison to compare the 27w 370 to the ~50w M2 Pro.

It's true that power efficiency is such a hard metric to compare, especially on laptops and across different operating systems, but that's the point I'm making with the rough figures we have available.