ARM A53/A57/T760 investigated - Samsung Galaxy Note 4 Exynos Review
by Andrei Frumusanu & Ryan Smith on February 10, 2015 7:30 AM ESTConclusion
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.
Facebook
Twitter
RSS
135 Comments
View All Comments
habbakuk87 - Wednesday, February 11, 2015 - link
I had like to thanks the writers for great in depth article, this is the kind of thing which has kept me coming to this site over the past many years.Keep up the good work.
Arbie - Wednesday, February 11, 2015 - link
Yes, this is a great article - knowledgeable and in-depth. Work like this is what keeps Anandtech way above the crowd. Thanks.joe_dude - Wednesday, February 11, 2015 - link
What it looks like to me is that they need to cap 4 big core load to 1.6 GHz, which would keep the thermals under control. Going by the chart, 1 core @ 1.9 GHz, 2 cores @ 1.8 GHz, 3 cores @ 1.7 GHz would work nicely for power consumption/heat as well. It seems Samsung and Qualcomm are setting the max frequency too high. That last 100 to 200 MHz requires a lot more voltage.joe_dude - Wednesday, February 11, 2015 - link
You look at the power consumption at 1.9 GHz vs. 1.6 GHz - 7.39w vs. 4.44w. That's the crux of the problem right there. 4 cores should not be running at such a high clock speed (and voltage needed to support it).PrinceGaz - Wednesday, February 11, 2015 - link
"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."That made me laugh as it is easily the most out of touch comment I've read in an AnandTech review.
It may be true for you as a reviewer sitting at home with the phone plugged into a USB charger running benchmarks that you feel the extra performance is worthwhile, but it will count for nothing when you use it in the real world and find your battery is dead earlier. Almost everyone with a smartphone today would rather have longer battery life instead of higher performance, because just like with PCs for some time now, the performance is already good enough.
Longer battery life trumps extra performance in smartphones now. I don't know why you want to put a positive spin on these higher performance but lower efficiency A57/A53 cores; I doubt ARM are paying you, but it seems they are a step backwards for people who use their phone primarily on the move, which includes most people.
patrickjchase - Wednesday, February 11, 2015 - link
From long experience with a variety of microarchitectures (including ARMs), I would guess that the latency/bandwidth "oddities" reflect differences in hardware prefetch. That's the most logical culprit among the list of changes that ARM provided.The hypothesis that the capability to dual-issue loads/stores impacts bandwidth to L2 and/or DDR seems questionable, because 4xA7 already has enough ld/st bandwidth to saturate both. Memory-limited code shouldn't see much impact due to issue-rule relaxation.
aryonoco - Wednesday, February 11, 2015 - link
Andrei and Ryan, thank you. I have not been impressed with anything Anandtech has published this much since the Original HTC One M7 review by Brian.I believe you guys have just published the most thorough, detailed, comprehensive review of every aspect of an ARM SoC. Short of working at a chip maker's lab, I don't think anyone is going to have any better exposure to the ARM ecosystem than what you guys have presented here.
Huge thanks for finally paying attention to the SoCs that don't make it to the North American market. I've been fascinated by their performance and power consumption metrics, it's great to finally have an authoritative view of them. I would love to have your take on some other SoCs in this regard as well, especially Cortex A17. There is not much coverage of Cortex A17 and I think, given the situation with big.LITTLE, a quad core well optimised Cortex A17 might actually be a hidden weapon that no one seems to be using.
Also very much looking forward to your coverage of overclocking/undervolting mobile devices. You guys are truly bringing AnandTech to the mobile industry.
Once again, thank you. To be honest, I've been a bit worried since Anand and Brian's departure about the direction of AT, and it's so good to see it thrive in such capable hands now.
Andrei Frumusanu - Wednesday, February 11, 2015 - link
I'm planning on reviewing the A17, but still in the process of securing a device. Hopefully in the near future.aryonoco - Wednesday, February 11, 2015 - link
On the subject of Javascript benchmarks and Chrome vs Stock browsers:Are we sure that all of the difference is indeed due to the optimized libraries that Samsung has developed, and that there is no benchmark-targeting optimization going on? After all, we saw what happend with Sunspider (and thanks for dropping it), it is impossible that they are not targeting Kraken and Octane as well?
Would it be feasible for Anandtech to develop its own proprietary javascript benchmark? It could answer a few of these questions.
tuxRoller - Wednesday, February 11, 2015 - link
This was an excellent read.Good detail, and enlightening investigation.
With regards to the power aware governor, you have to realize that it's a very hard problem. One that no one has managed, yet (iirc, huawei has claimed that their kernel has such a scheduler, but, you've seen how well it works), for general loads. Yes, there are many ideas but, as you've surmised, board implementations can drastically change assumptions.
BTW, power collapse appears to just be the arm term for the state under which cpuidle takes over for that core. So, it's not actually powered off, thus hotplug would still be needed.
For an overview of the domain see: http://lwn.net/Articles/482344/
Some useful links:
https://rt.wiki.kernel.org/index.php/Energy_Aware_...
https://lkml.org/lkml/2014/5/23/621