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Comment by jackcviers3 | Hacker News Reader

So, like nice[1], except the developer sets the level of importance ahead of time? Makes sense, as long as I can reprioritize if needed.

1. https://en.wikipedia.org/wiki/Nice_(Unix)

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It's nice but with additional limitations - on a normal Unix system even if you nice everything to the lowest level possible they'll still take over all cores. This limits things below a certain nice level to the efficiency cores, meaning that the performance cores are always available for foreground action.

So nice + taskset[1]?

1: https://linux.die.net/man/1/taskset

Seems so. Just that it works "automagically" and reserves some cores for certain priority groups. Maybe one can write a script/daemon that `taskset`s all tasks with a certain niceness range (or by additional rules) to a few "background cores" and everything else to the "interactive cores"?

On Linux you might also get some problems with kworker threads landing in the wrong group, but I'm not that much into Kernel internals I've to admit.

Could do it with SystemD AllowedCPUs functionality, but that's not dynamic

These days you'd probably want to use cpuset cgroups so you don't have to worry about individual processes.

Of course the applications (programmers of the applications) need to declare their "nice" levels correctly - they can't be greedy

Nothing has ever stopped Apple from pinning indexing work to specific cores. They just didn't give a shit.

I suspect they did it less for performance and more for energy savings - this prevents the scheduler from moving a background process to a performance core (which a naive one would do if it saw the performance core underutilized).

It's always done this but the effect wasn't visible on x86.

Maybe like the big.little cores of many ARM CPU in Android phone?

I'm not familiar with Android APP, maybe there are similar APIs in Android?

It's the same big.Little concept, slightly tweaked to allow this QoS work, I believe most of it was then used on Android but I doubt that Android uses the APIs well if they exist.

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