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Comment by 988747 | Hacker News Reader

So why put efficiency cores in the desktop processor at all?

A desktop runs a lot of low priority processes. The efficiency cores can be given all those processes. This means some low priority thread will get scheduled on a performance core and bust the cache.

There's also plenty of time where the system has low intensity use or is idle. The efficiency cores let things like receiving notifications or checking e-mail happen for very little power draw. Fans only need to run during intense use and the system can be quiet the rest of the time.

The guys have split the traditional UI thread and the background thread down to the silicon.

Who knows, maybe the UI thread only needs access to the graphics card, and the background thread only access to network. It would save a lot of interrupt loops.

> Fans only need to run during intense use and the system can be quiet the rest of the time.

This is a bigger deal than it might seem. Fans running means that dust is accumulating in the machine at an accelerated rate, even if you have filters in place. The less the fans have to run, the less dust accumulates, and the longer cooling functions near-peak. A tower that sees sporadic heavy usage especially stand to benefit from fan minimization.

As has been mentioned elsewhere, devoting some cores to background tasks and reserving the others for higher-priority stuff also makes the system feel more responsive.

See, for example, this article from yesterday: https://eclecticlight.co/2021/05/17/how-m1-macs-feel-faster-...

Long story short, segregating background work from foreground work means that Spotlight indexing won't cause the UI to become sluggish. I'm guessing it also tends to be more cache-friendly.

But separating the background work doesn't actually require efficiency cores. With 40 performance cores, you could still dedicate 4 or 8 of them to "background" processes only. As that article you linked shows, the background processes would simply complete more quickly without affecting interactive work on the machine.

performance cores are physically larger than the efficiency ones, by about 3-4x. I'm sure there are other tradeoffs cache size like too. So would you rather have 32 performance cores and 8 efficiency or 34 performance?

Consuming 1/10 as much power would also have thermal advantages for the die overall, and segregating them onto a separate L2 cache from the performance cores would help with that cache friendliness situation, different allocations of logic units means you can tailor them toward different kinds of workloads. . . I'm no CPU designer, so I really can't speak with authority here, but I can at least see several possible reasons why it would make sense even when you aren't worried about battery life.

In upper end extreme case, using 8 HE Core instead of 8 HP Core saves you 24 to 32W. Those 32W could allow more GPU usage or some other part of system such as ISP or NPU.

At the end of the day you will still need HE Core, they just aren't as important comparing to a Battery devices.

Not to mention Marketing, Die Size cost consideration.

It still nice to reduce power consumption and heat production when running idle.

To reduce the need for noisy cooling.

Heat.

To expand on that:

The design challenge of high-performance CPUs today is heat. Too much heat induces throttling. Putting low-priority stuff onto efficiency cores reserves the power budget of the SoC for high-priority tasks.

https://arstechnica.com/gadgets/2021/05/apples-m1-is-a-fast-...

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