According to an AMD engineer I asked at the time, when they evaluated Ryzen/K12, it was "maybe" a 15% advantage for ARM depending on scenarios.
The efficiency came solely from the frontend which is a lot heavier on x86, and stay up longer because decoding is way more complex. The execution units were the same (at least mostly, I think, might be misremembering) so once you are past the frontend there's barely any difference in power efficiency.
The efficiency came solely from the frontend which is a lot heavier on x86, and stay up longer because decoding is way more complex. The execution units were the same (at least mostly, I think, might be misremembering) so once you are past the frontend there's barely any difference in power efficiency.