The new Samsung Galaxy S4 are sold in two configurations that differ in the processor. It is assumed that the Samsung Exynos 5 Octa was very interesting characteristics of energy efficiency, but now are data that make it clear that this efficiency is lower than expected.
Blame is not the processor itself in reality, but is the Linux kernel which due to a partial support of this processor You can not take advantage of different planning methods and resource allocation that would take much more party of Samsung Exynos 5 Octa.
We knew that the octo – core processor the Samsung Galaxy S4 could operate with four cores A15 either or with four cores A7 according to the required workload, but in reality this way of work It is not the most efficient.
Three modes of work, only one is used
As explained the user AndreiLux on XDA Developers, big architecture forums. Has a LITTLE of three modes of operation:
- Cluster migration: the workload of our mobile device determines if used the more powerful quad-core (processor “big” A15) or the four aimed at light loads (A7, “LITTLE” processor). This is the mode of operation that is always used in Exynos 5 Octa.
- Migration of nuclei: something more complex than the previous one. When the load increases, only change the nuclei of the LITTLE processor whose load exceeds the capacity of those nuclei. Thus, we could have other three A7 in operation, or any other combination of quad-core running single core A15.
- Heterogeneous multiprocessing: More complex still. You need the kernel scheduler difference kernels A15 of the A7, something which at the moment cannot do, since it is all cores in the same way. The idea would be not to have to always use four cores if a task can use only one or two cores, combining the A7 with the A15, which would allow a perfect efficiency in each case.
Take advantage of the second mode of operation would require a new driver DVFS (Dynamic Voltage and Frequency Scaling), which is the component that determines if the charge needed should be assigned to a type of core or the other. For the third mode of heterogeneous multiprocessing, the problem lies in the Linux kernel and its current Planner, one of the more complex elements of this basic component of Android.
There is no change in the medium term
It will be difficult to see take advantage of these advanced options in the current generation of processors, since the inclusion of planners is very unusual and only advanced users do compiling their own kernels.
Perhaps some “Chef” of ROMs You can make some of these improvements, but the truth is that today the performance of Samsung Exynos 5 Octa seems hampered by own kernel and drivers used in Android support.