This is not actually the case: this can be changed within Logic Pro's settings.

You can set the number of cores utilized by default in the settings, yes. But Logic will only fully utilize the performance cores. I made a mistake and over-stated by saying it would only use performance cores. The conclusion isn't different though. M1 Pro will handle more tracks currently.

See here: https://youtu.be/FSqX4bt9to4?si=6KBj5vNra3rEITWI&t=439

Are you saying the performance regression isn't real because there's a workaround for the bug?

Is that possible? You can set priority to background and your process will be restricted to E cores, but last I checked other processes will favor P cores but will be spilled to E if everything is loaded. I also don’t remember an API to query the core layout (to only spawn as many workers as there are P cores).

But maybe that was added since?

IIRC there are sysctls that list the number of cores of each type, and their cache sizes. So an application can check how many P cores there are, and choose to only spawn that many threads.

Yeah but it just means that software needs to tweak some parameters on M3 to slow spilling to E cores. In fact, a good system would always spill to E cores ands just let completion rates drive acceptance of work stealing.

That's crazy talk! You must be holding it wrong :)