The Samsung Exynos 7420 Deep Dive - Inside A Modern 14nm SoC

Conclusion

Samsung’s Exynos 7420 is a major stepping stone for Samsung LSI. While on a functional and IP basis the chipset hasn’t seen substantial differentiation from its predecessor, it’s on the actual physical implementation and manufacturing process that the new SoC has raised the bar.

On the CPU side of things, we saw some performance improvements due to slightly higher clocks and what seems to be a better cache implementation, especially the big CPU cluster. Equally on the big cluster Samsung has played it safe and has gone for power efficiency rather than aiming for maximum achievable clocks. ARM’s Cortex A57 in the Exynos 5433 was already overshooting performance over its direct competitor, the Snapdragon 805, so there was no need for the Exynos 7420 to push the clocks much higher. And this is a good design decision for the new SoC as both maximum power as well as power efficiency have improved by a lot. With the new part now using 35-45% less power at equal frequencies it now has the required TDP and efficiency to be placed in thin smartphones such as the Galaxy S6.

I think Samsung could have even gotten away in performance benchmarks by keeping the chip at up to only 1.9GHz to keep power consumption below the 1W per core mark. This would have slightly improved efficiency on high loads as the small 10% performance degradation would have been worth the 26% power improvement.

In the review of the Exynos 5433 I was very up front about my disappointment with that SoC’s software and power management as it showed very little optimization and the degradation in real-world use-cases was measurable. This time around, it seems Samsung Electronics did a better job at properly configuring the scaling parameters of the SoC’s power management. Gone are the odd misconfigurations, and with them also most of the inefficient behaviors that we were able to measure on the big.LITTLE SoC’s predecessor. While there’s still plenty of room for improvement such as an eventual upgrade to an energy-aware scheduler, it currently does the job in a satisfactory way.

On the GPU side of things we saw sort of a two-sided story; The good side is that the Exynos 7420’s Mali T760MP8 combined with the 14nm process not only makes this the fastest SoC we’ve seen in a smartphone but also currently the most efficient one that we measured. The bad side of the story is that while it’s the most efficient SoC, the performance and power again overshoots the sustainable TDP of the phone as it will inevitably thermal throttle to lower frequency states during active usage. Over the last few generations this issue grew worse and worse as semiconductor vendors and OEMs tried to boost their competitive position in benchmark scoreboards.

While for the CPU there are real-world uses and performance advantages of having overdrive frequencies above the sustainable TDP, one cannot say the same for the GPU. Samsung is not alone here in this practice as also Qualcomm and many others employ overpowered configurations that make no sense in the devices they ship in. Having a reasonably balanced SoC has become more of the exception than the rule. One can argue that these are high-performance designs that are also meant to also go into tablets and larger form-factors, and SoC vendors should subsequently not be at the ones at receiving end of the blame – it would then be the OEM’s responsibility to properly configure and limit power via software when using the parts in smaller devices. Ultimately, I’d like to see this practice go away as it brings only disadvantages to the end-consumer and leads to an inconsistent gaming experience with reduced battery life.

The Galaxy S6 with the Exynos 7420 is among the first wave of devices to feature LPDDR4 memory. While the performance improvement was nothing ground-breaking, with the boost coming at an average 18-20% in GFXBench, it’s mostly the efficiency that should have the biggest impact on a device’s experience. While I wasn’t able to fully quantize this advantage during measurement due to the complexity of the task, the theoretical gains show that improvements in daily use-cases should be substantial.

Overall, the big question is how good the Exynos 7420 finally is. The verdict on a SoC vastly depends on the competing alternative options available at the time. For the better part of 2015 this will most likely be Qualcomm’s Snapdragon 810 and to a lesser part the Snapdragon 808. In this piece I was already able to show GPU numbers of the S810 and the results unfortunately showed no improvement over the Snapdragon 805, which the Exynos 7420 already beats both in performance and power. While I already have CPU numbers for the 810, we weren’t quite ready to include these in this piece as they’ll warrant a more in-depth look in a separate article. Readers who have already read our review of the HTC M9 will already know what to expect as the SoC just wasn’t able to perform as promised, and I can confirm that the efficiency disadvantage relative to the Exynos 7420 is significant.

Ultimately, this leaves the Exynos 7420 without real competition. Samsung was able to hit it out of the park with the new 14nm design and subsequently leapfrogged competing solutions. For the near future, the Exynos 7420 comfortably stands alone above other Android-targeted designs as it sets the new benchmark for what a 2015 SoC should be.