this post was submitted on 23 Oct 2023
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Apple

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How does macOS manage virtual cores on Apple silicon? (eclecticlight.co)
submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/apple_enthusiast
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One of the most distinctive features of Apple silicon chips is that they have two types of CPU core, E (Efficiency) cores that are energy efficient but slower than the P (Performance) cores, which normally run much of the code in the apps we use. Apps don’t decide directly which cores they will be run on, that’s a privilege of macOS, but they register their interest by setting a Quality of Service, or QoS, which is then taken into account when they’re scheduled to run. With the introduction of Game Mode in Sonoma, CPU scheduling can now work differently, with E cores being reserved for the use of games. This article looks at another atypical situation, when running a macOS virtual machine (VM) assigned a set number of virtual cores. How does macOS Sonoma handle that?

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[–] [email protected] 15 points 1 year ago (11 children)

One of the most distinctive features of Apple silicon chips is that they have two types of CPU core, E (Efficiency) cores that are energy efficient but slower than the P (Performance) cores, which normally run much of the code in the apps we use.

Just want to point out that this is far from unique to apple. Lots of Arm processors have this. I think my first phone that had it was the OnePlus 2, which launched in 2015.

I would honestly be surprised if any major smartphone didn't have this.

[–] GrayBoltWolf -3 points 1 year ago (1 children)

Also most modern x86 desktop CPUs have this too.

[–] abhibeckert 3 points 1 year ago* (last edited 1 year ago) (2 children)

As far as I know not to the same degree? For example I'm pretty sure Apple's efficiency cores don't do speculative execution or at least don't do much of it.

AFAIK the x86 chips mostly just reduce the clock speed don't they?

[–] [email protected] 0 points 1 year ago (1 children)

x86-64 doesn’t need efficiency cores because unlike ARM, it doesn’t care about limiting power draw.

ARM’s main appeal has always been ability to compute with minimal current (I think the first ARM processor consumed no power).

[–] [email protected] 2 points 1 year ago* (last edited 1 year ago) (2 children)

I think the first ARM processor consumed no power

Now that would be some efficiency aight.

I recall something about operating on leak current alone, which is probability where you got that from.

[–] cashews_best_nut 3 points 1 year ago

Don't try this at home. You could cause an infinitly powered electro-black-hole.

[–] [email protected] 0 points 1 year ago (1 children)

@Skelectus @ultratiem yes, that happened. It first worked on residual energy from the board it was on. It was a funny accident actually. They forgot to turn on the power supply, but it was working.

[–] [email protected] 1 points 1 year ago

That can't be quite right either, as it would be eaten immediately.

I looked it up, most specific I could find is this quote:

...leakage from the power rails leading to the I/O chip

Not sure how accurate this is, but the power has to originate from something that is actively powered.

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