alt Hacker NewsCan't Windows/Linux pin background threads to specific cores on Intel too? So that your foreground app isn't slowed down by all the background activity going on? Or there's something else to it that I don't understand. I thought E cores' main advantage is that they use less power which is good for battery life on laptops. But the article makes it sound like main advantage of Apple Silicon is that it splits foreground/background workloads better. Isn't it something that can already be done without a P/E distinction?
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It’s both.
Multithreading has been more ubiquitous in Mac apps for a long time thanks to Apple having offered mainstream multi-CPU machines very early on (circa 2000), predating even OS X itself, and has made a point of making multithreading easier in its SDK. By contrast multicore machines weren’t common in the Windows/x86 world until around the late 2000s with the boom of Intel’s Core series CPUs, but single core x86 CPUs persisted for several years following and Windows developer culture still hasn’t embraced multithreading as fully as its Mac counterpart has.
This then made it dead simple for Mac developers to adopt task prioritization/QoS. Work was already cleanly split into threads, so it’s just a matter of specifying which are best suited for putting on e-cores and which to keep on P-cores. And overwhelmingly, Mac devs have done that.
So the system scheduler is a good deal more effective than its Windows counterpart because third party devs have given it cues to guide it. The tasks most impactful to the user’s perception of snappiness remain on the P-cores, the E-cores stay busy with auxiliary work and keep the P-cores unblocked and able to sleep more quickly and often.
It's the combination of the two that yields the best of both worlds.
Android SoCs have adopted heterogenous CPU architectures ("big.LITTLE" in the ARM sphere) years before Apple, and as a result, there have been multiple attempts to tackle this in Linux. The latest, upstream, and perhaps the most widely deployed way of efficiently using such processors involves using Energy-Aware Scheduling [1]. This allows the kernel to differentiate between performant and efficient cores, and schedule work accordingly, avoiding situations in which brief workloads are put on P cores and the demanding ones start hogging E cores. Thanks to this, P cores can also be put to sleep when their extra power is not needed, saving power.
One advantage macOS still has over Linux is that its kernel can tell performance-critical and background workloads apart without taking guesses. This is beneficial on all sorts of systems, but particularly shines on those heterogenous ones, allowing unimportant workloads to always occupy E cores, and freeing P cores for loads that would benefit from them, or simply letting them sleep for longer. Apple solved this problem by defining a standard interface for the user-space to communicate such information down [2]. As far as I'm aware, Linux currently lacks an equivalent [3].
Technically, your application can still pin its threads to individual cores, but to know which core is which, it would have to parse information internal to the scheduler. I haven't seen any Linux application that does this.
[1] https://www.kernel.org/doc/html/latest/scheduler/sched-energ...
[2] https://developer.apple.com/library/archive/documentation/Pe...
[3] https://github.com/swiftlang/swift-corelibs-libdispatch?tab=...
Similarly, are there any modern benchmarks of the performance impact of pinning programs to a core in Linux? Are we talking <1% or something actually notable for a CPU bound program?
I have read there are some potential security benefits if you were to keep your most exploitable programs (eg web browser) on its own dedicated core.
Pinning exists, but the interesting part is signal quality: macOS gets consistent “urgency” signals (QoS) from a lot of frameworks/apps, so scheduling on heterogeneous cores is less guessy than infer from runtime behavior.
Yes, it's the job of the scheduler
Linux yes, of course.
One thing that distinguishes macOS here is that the mach kernel has the concept of “vouchers” which helps the scheduler understand logical calls across IPC boundaries. So if you have a high-priority (UserInitiated) process, and it makes an IPC call out to a daemon that is usually a low-priority background daemon, the high-priority process passes a voucher to the low-priority one, which allows the daemon’s ipc handling thread to run high-priority (and thus access P-cores) so long as it’s holding the voucher.
This lets Apple architect things as small, single-responsibility processes, but make their priority dynamic, such that they’re usually low-priority unless a foreground user process is blocked on their work. I’m not sure the Linux kernel has this.