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And phone CPUs can be more complex than most desktops, afaik big.LITTLE is fairly common (multi core, with different performance / power tradeoffs between the c
by tonfa 8y ago
And phone CPUs can be more complex than most desktops, afaik big.LITTLE is fairly common (multi core, with different performance / power tradeoffs between the cores).
https://lwn.net/Articles/501501/ https://lwn.net/Articles/501501/ has some pointers.
- wolf550e 8y agoI was just saying the low end chips have only "little" cores, no "big" cores, but they are still multi-core. AFAIK nobody makes single core Cortex A chips. Single core Cortex M chips are made, but those are really puny.
- ansible 8y agoHilariously, it is common to see some SoCs, like the i.MX8, have Cortex-A and Cortex-M cores. You can do fun stuff like run different operating systems on them too. They can be used for real-time applications, safety-critical functions, etc.. And by "fun" I mean not-fun, because you've got multiple build processes and releases to manage.
- wolf550e 8y agoBut I think that's not used as a multiprocessor, with threads getting scheduling on either (or both) depending on power policy. The embedded cores are, I think, used as separate systems running separate OS that happen to have access to the same DRAM, like a peripheral that can do DMA. Thinking of running that as a single multiprocessing system I'm reminded of the bug caused by Samsung doing big.LITTLE with cores that have the same instruction set but differently sized cache lines: https://news.ycombinator.com/item?id=12481700 https://news.ycombinator.com/item?id=12481700
- ansible 8y ago> But I think that's not used as a multiprocessor, with threads getting scheduling on either (or both) depending on power policy. The embedded cores are, I think, used as separate systems running separate OS that happen to have access to the same DRAM, like a peripheral that can do DMA. Right, I didn't mean to imply otherwise.
- brandmeyer 8y agoThere are variations on this theme where the two types of cores are also cache coherent with each other.
- Twirrim 8y agobig.LITTLE is fascinating, and I'm somewhat curious to see if Apple tries to do something along those lines as it supposedly pushes towards ARM chips in their machines. Google have added some interesting stuff to Android to help it learn over time if tasks should be allocated to the bigger cores or the lower powered smaller ones, based on all sorts of metrics, and I believe this stuff is making its way upstream. There's certainly some really interesting potential around that.
- wolf550e 8y agoApple chips are big.LITTLE too, at least since the 2016 A10 in the iPhone7. https://en.wikichip.org/wiki/apple/ax/a12 https://en.wikichip.org/wiki/apple/ax/a12 https://en.wikichip.org/wiki/apple/ax/a10 https://en.wikichip.org/wiki/apple/ax/a10 https://www.anandtech.com/show/13392/the-iphone-xs-xs-max-review-unveiling-the-silicon-secrets/2 https://www.anandtech.com/show/13392/the-iphone-xs-xs-max-re...
- Twirrim 8y agoSure, I should be clear I was thinking about OSX and laptops/desktops, rather than mobile devices.