So the first question for the Google Silicon team is: what's up with this core layout?
Carmack's explanation is that the dual-X1 architecture is a play for efficiency at "medium" workloads. "We focused a lot of our design effort on how the workload is allocated, how the energy is distributed across the chip, and how the processors come into play at various points in time," Carmack said. "When a heavy workload comes in, Android tends to hit it hard, and that's how we get responsiveness."
This is referring to the "rush to sleep" behavior most mobile chipsets exhibit, where something like loading a webpage has everything thrown at it so the task can be done quickly and the device can return to a lower-power state quickly.
"When it's a steady-state problem where, say, the CPU has a lighter load but it's still modestly significant, you'll have the dual X1s running, and at that performance level, that will be the most efficient," Carmack said.
He gave a camera view as an example of a "medium" workload, saying that you "open up your camera and you have a live view and a lot of really interesting things are happening all at once. You've got imaging calculations. You've got rendering calculations. You've got ML [machine learning] calculations, because maybe Lens is on detecting images or whatever. During situations like that, you have a lot of computation, but it's heterogeneous."
A quick aside: "heterogeneous" here means using more bits of the SoC for compute than just the CPU, so in the case of Lens, that means CPU, GPU, ISP (the camera co-processor), and Google's ML co-processor.
Carmack continued, "You might use the two X1s dialed down in frequency so they're ultra-efficient, but they're still at a workload that's pretty heavy. A workload that you normally would have done with dual A76s, maxed out, is now barely tapping the gas with dual X1s."
The camera is a great case study, since previous Pixel phones have failed at exactly this kind of task. The Pixel 5 and 5a both regularly overheat after three minutes of 4K recording. I'm not allowed to talk too much about this right now, but I did record a 20 minute, 4K, 60 FPS video on a Pixel 6 with no overheating issues. (I got bored after 20 minutes.)
