It seems Samsung's implementation of ARM's new big.LITTLE heterogeneous computing architecture isn't entirely what people (and perhaps Samsung too) hoped it would be.
Samsung has been advertising that their newest flagship Galaxy S4 packs an octa core processor. While technically true, the implementation isn't. At best only four of the eight available cores are working, making the S4 another quad core running phone. Samsung justified the use of an octa core design for higher energy efficiency, and, thus, leading to longer battery life. Popular android kernel developer AndreiLux is convinced, however, that Samsung's implementation is simply awful. In the words of the wise developer:
The problem here is more driver related than anything. Currently, the linux kernel doesn't differentiate between the different architecture based cores and thus treats them all equally. As a result, big.LITTLE's MP mode (it's most powerful running mode) is broken, although Samsung's Exynos 5 Octa silicon supports it. If implemented correctly, all the physical cores (true octa core phone in that case) will work in tandem, with threads having higher priority or computational intensity simply allocated to the bigger, and more powerful cores.
Perhaps a new Linux kernel and associated updates from Samsung might change this over the months, and the Galaxy S4 might actually end up showing big performance gains and battery life improvements as a result.