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Comment by m_a_g | Hacker News Reader

An 8 core processor on a Macbook Air that is also energy efficient? That is truly impressive. I never thought I would consider using Macbook Airs after all the years of using Macbook Pros, but Apple surprises me once again.

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It's 8-core, but they're 4 performance and 4 low-power cores, so it's not your normal 8-core chip. It's more like a big.LITTLE chip.

Anyone know how you interact with these cores as a developer/user? Say if I'm running some C code with OpenMP parallelism, can I bind it to three of the fast cores?

Binding to specific cores is not exposed to userspace, but you can influence which kinds of cores it's likely to be run on by setting thread priorities and QoS classes.

With ARM, yes, and you can also selectively turn on and off cores. For example when travelling with my pinebook pro I turn the big cores off to drastically improve battery life. However it's up to Apple to expose this functionality, and we all know how much control apple wants you to have of the computers you "license" from them.

WRT the pinebook, i didnt know it could do that. can it be done at runtime or do you have to change it at boot time?

They can be onlined or offlined at any time,

To offline a core:

echo 0 > /sys/devices/system/cpu/cpuN/online

To online a core:

echo 1 > /sys/devices/system/cpu/cpuN/online

Where cpuN is 0-4. Keep in mind there's always one core you cannot disable to process interrupts.

Very cool, thank you.

That sounds awesome. Sounds really fun to hack around. I might buy a Pinebook

The macOS SDK exposes a processor affinity API that you can program against.

There isn't an option like taskset on Linux to pin or move tasks among different cores, or like anything that's exposed in Linux's sysfs.

Seems pretty clear they're using big.LITTLE-style low-power and high-power cores on the same chip.

No fan however, is impressive....

But it can't sustain max performance. That is reserved for the MacBook Pro with a fan.

4 high-power and 4 low-power cores.

At 9:15 of the keynote they claim that the "high-efficiency" cores are as powerful as the outgoing dual-core MacBook Air's cores. Seems pretty good to me.

Agreed, but I wish I knew the numbers behind those statements.

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