Samsung’s Octa-Core not as energy efficient as we thought??
So we all know that Samsung’s Octa is their big technical achievement this year at least that is what they like us to think.
The well-known and respected Kernel Dev AndreiLux discovered that the octa isn’t fully energy-efficient optimized. And he said Samsung has chosen the most awful implementation of the Octa-Core possible.
The Octa was advertised as followed:
This is a unofficial leaked presentation from their semiconductor business. Here you clearly can see how the cores should be working.
So what did AndreiLux find out, well he found out that the cores only can work in clusters so only 4 A7’s or 4 A15’s at the time.
I contacted him on XDA and asked him for some clarity, I will quote some of his message.
“Basically there are three modes of operation of big.LITTLE:
Cluster migration: When load rises, just like when a phone increases is frequency per DVFS, all the cores will jump from the LITTLE processor to the big one. You either have 4 A7 cores or 4 A15 cores online.
Core migration: When load rises, it will only jump those cores from the LITTLE processor whose load exceeds the capacity of the A7 cores: You can have a single A15 online with 3 A7’s on. Or any other combination of a total of 4 processors.
HMP (Heterogeneous Multi-Processing): This is a vastly more complex working mechanism, and its implementation is also an order of magnitude more sophisticated. It requires the kernel scheduler to actually be aware of the differentiation of between the A7 and A15 cores. Currently, the Linux kernel is not capable of doing this and treats all CPUs as equals. This is a problem since we do not want to use the A15 cores when a task can simply me processed on an A7 core with a much lower power cost.”
It seems driver related and it is way to difficult to comprehend for us normal folks, so I will not go into the technical details. If you are still interested in the technical details please follow this link.
So is this thing not finished yet, is it a hardware limitation or is it something else, well only Samsung knows and lets hope they will come with an answer. But as always do not count on it, cause Samsung hasn’t got a good reputation if it comes to the developer community.
I will stop with a quote from him which seems right at his place here.
“Matter of fact is: The CPU isn’t running under optimal power efficiency right now, you cannot argue with that.”
Thank you AndreiLux!
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