Samsung's Exynos 5 eight-core processor may not actually function as an eight-core, but as a quad-core instead, according to an Android kernel developer. The eight-core processor, featured in select Samsung Galaxy S4 device is also expected to be featured in the Samsung Galaxy Note 3.
In devices such as the Galaxy S4 and the upcoming Galaxy Note 3, multi-core chips execute multiple program instructions at once. Quad-core chips have four cores and octa-cores have eight. Just because the octa-core can execute instructions twice as fast, it doesn't always mean that it can receive instruction from the RAM at that same speed.
Android developer AndrieLux reported that in the case of the Exynos 5 octa-core, only four cores function at a time. He claims that the Linux kernel, which Android is based on, doesn't differentiate between the architecture-based cores. The Exynos 5 Octa utilizes ARM big.LITTLE technology with a quad-core ARM Cortex-A7 CPU and a quad-core Cortex-A15 CPU, for a total of eight cores.
As reported by Tom's Hardware, AndrieLux said the implementation of the big.Little driver is flawed. Updating the Linux kernel will resolve the issues within the Exynos 5 octa-core and result in performance and battery improvements. Users who are using the Exynos 5 octa-core variant of the Galaxy S4 may be only really using four cores. When the Galaxy Note 3 makes its debut on the market, hopefully the Linux kernel will be updated by then.
AndrieLux noted the following three key events occur:
Cluster migration: When the amount of computational work the CPU has to perform (load) rises, the cores jump from the LITTLE processor to the big processor. Either the four A7 cores or four A15 cores are online.
Core migration: When load rises, it selectively jumps to the cores from the LITTLE processor whose load exceeds that capacity of the A7 cores. When this happens, there's only one A15 online with three A7′s or any other combination that totals four processors.
Heterogeneous Multi-Processing (HMP): Linux kernel's scheduler must know the difference between the four A7 cores from the four A15 cores. Linux kernel currently recognizes all CPUs as equals. This becomes an issue, since it's not necessary to use the power hungry A15 cores when the less power-consuming A7 can be used to complete a task.
