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Comment by astrange | Hacker News Reader

General term is asymmetric multiprocessing, which goes back a few more decades:

https://en.wikipedia.org/wiki/Asymmetric_multiprocessing

IIRC big.LITTLE implementations tended to have cores that didn't support the same instruction sets, meaning you couldn't migrate tasks between them if you needed to. Kind of like how laptops could switch between integrated and discrete GPUs, but some users would need to switch to the discrete GPU to use an external monitor even if they didn't want the power hit.

Also, "big.LITTLE" is a pretty strange brand name.

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I think the term you're going for here is heterogeneous multi-processing/computing, not asymmetric multiprocessing:

https://en.wikipedia.org/wiki/ARM_big.LITTLE#Heterogeneous_m...

https://en.wikipedia.org/wiki/Heterogeneous_computing

It even lists big.LITTLE there as a typical example in the second article. big.LITTLE itself never had different ISAs as far as I could tell, just scheduling caveats that lead to efficiency tradeoffs, like the first article mentions.

My understanding of "heterogenous computing" is that it's more about splitting a task across a CPU and coprocessors, or writing the same code to target both. Asymmetric means there's multiple CPU cores but they're not equally performant.

big.LITTLE is typically cores with the same architectural features, just different performance due to different microarchitecture. A7/A15/A17, or A53/A57/A72, or A55/A76.

This let them run the same code, even the same system level code. The scheduler only had to optimize performance, without tasks being pinned to one core or another for correctness.

This is the case in Intel 12th gen: P cores support AVX512, E cores do not. Instead of allowing OS-level support, you could gain back AVX512 by disabling E cores. Intel ended up disabling that feature in hardware later though.

This was honestly a pretty surprising mistake for a big player like Intel. Quite a big oversight in my opinion. The fact that the OS will migrate processes from big cores to little cores should not be a surprise, given that it is basically necessary for the power savings to be realized. That effectively necessitates having the same ISA on both the big and little cores. It's not like desktop class operating systems haven't been running on these types of cores for over a decade.

Not to be confused with Little Big - https://en.wikipedia.org/wiki/Little_Big_(band)

Not to be confused with LittleBigPlanet.

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