ARM A53/A57/T760 investigated - Samsung Galaxy Note 4 Exynos Review

Conclusion

Samsung's System LSI business had a rough two years as their decision to go with ARM's big.LITTLE SoC architecture cost them a lot of market share, thanks in part to immature software and implementation issues. Usually in the past Samsung's own Exynos SoCs were regarded as the more performant variant given the choice of Qualcomm's Scorpion CPU based solutions. This changed as the Exynos 5410 came out with a malfunctioning CCI, crippling the chip to the most battery inefficient operating mode of big.LITTLE.

Qualcomm's Snapdragon 800 capitalized on the new 28nm HPM manufacturing process, along with the advantage of being able to offer an integrated modem solution, and has dominated the market ever since. It's only now that Samsung is able to recover as the new 20nm manufacturing process allowed them to catch up and start to offer their own Exynos SoC in more variants of its products, a trend that I expect to continue in Samsung's future lineup.

The Note 4 with the Exynos 5433 is the first of a new generation, taking advantage of ARM's new ARMv8 cores. On the CPU side, there's no contest. The A53 and A57 architectures don't hold back in terms of performance, and routinely outperform the Snapdragon 805 by a considerable amount. This gap could even widen as the ecosystem adopts ARMv8 native applications and if Samsung decides to update the phone's software to an AArch64 stack. I still think the A57 is a tad too power hungry in this device, but as long as thermal management is able keep the phone's temperatures in reign, which it seems that it does, there's no real disadvantage to running them at such high clocks. The question is whether efficiency is where it should be. ARM promises that we'll be seeing much improved numbers in the future as licensees get more experience with the IP, something which we're looking forward to test.

On the GPU side, things are not as clear. The Mali T760 made a lot of advancements towards trying to catch up with the Adreno 420 but stopped just short of achieving that, leaving the Qualcomm chip a very small advantage. I still find it surprising that the Mali T760 is able to keep up at all while having only half the available memory bandwidth; things will get interesting once LPDDR4 devices come in the next few months to equalize things again between competing SoCs. Also ARM surprised us with quite a boost of GPU driver efficiency, something I didn't expect and which may have real-world performance implications that we might not see in our synthetic benchmarks.

It's the battery life aspect that I think it's most disappointing to me. It's a pity that Samsung didn't go through more effort to optimize the software stack in this regard. When you are able to take advantage of vertical integration and posses multi-billion dollar semiconductor manufacturing plants with what seem to be talented SoC design teams, it's critical to not skimp out on software. I might be a bit harsh here given that the battery disadvantage was just 12% in our web-browsing test and might be less in real-world usage, and the GPU battery efficiency seems neck-and-neck. Still, it's the wasted potential from a purely technical perspective that is disheartening.

This is definitely a wake-up call to ARM and their partners as well. If the software situation of big.LITTLE isn't improved soon I'm fearing that ship will have sailed away, as both Samsung and Qualcomm are working on their custom ARMv8 cores.

So the question is, is it still worth to try and get an Exynos variant over the Snapdragon one? I definitely think so. In everyday usage the Exynos variant is faster. The small battery disadvantage is more than outweighed by the increased performance of the new ARM cores.