GPU Power Consumption and Thermal Stability

GPU Power Consumption

The Kirin 960 adopts ARM’s latest Mali-G71 GPU, and unlike previous Kirin SoCs that tried to balance performance and power consumption by using fewer GPU cores, the 960’s 8 cores show a clear focus on increasing peak performance. More cores also means more power and raises concerns about sustained performance.

We measure GPU power consumption using a method that’s similar to what we use for the CPU. Running the GFXBench Manhattan 3.1 and T-Rex performance tests offscreen, we calculate the system load power by subtracting the device’s idle power from its total active power while running each test, using each device’s onboard fuel gauge to collect data.

GFXBench Manhattan 3.1 Offscreen Power Efficiency
(System Load Power)
  Mfc. Process FPS Avg. Power
LeEco Le Pro3 (Snapdragon 821) 14LPP 33.04 4.18 7.90 fps/W
Galaxy S7 (Snapdragon 820) 14LPP 30.98 3.98 7.78 fps/W
Xiaomi Redmi Note 3
(Snapdragon 650)
28HPm 9.93 2.17 4.58 fps/W
Meizu PRO 6 (Helio X25) 20Soc 9.42 2.19 4.30 fps/W
Meizu PRO 5 (Exynos 7420) 14LPE 14.45 3.47 4.16 fps/W
Nexus 6P (Snapdragon 810 v2.1) 20Soc 21.94 5.44 4.03 fps/W
Huawei Mate 8 (Kirin 950) 16FF+ 10.37 2.75 3.77 fps/W
Huawei Mate 9 (Kirin 960) 16FFC 32.49 8.63 3.77 fps/W
Galaxy S6 (Exynos 7420) 14LPE 16.62 4.63 3.59 fps/W
Huawei P9 (Kirin 955) 16FF+ 10.59 2.98 3.55 fps/W

The Mate 9’s 8.63W average is easily the highest of the group and simply unacceptable for an SoC targeted at smartphones. With the GPU consuming so much power, it’s basically impossible for the GPU and even a single A73 CPU core to run at their highest operating points at the same time without exceeding a 10W TDP, a value more suitable for a large tablet. The Mate 9 allows its GPU to hit 1037MHz too, which is a little silly. For comparison, the Exynos 7420 on Samsung’s 14LPE FinFET process, which also has an 8 core Mali GPU (albeit an older Mali-T760), only goes up to 772MHz, keeping its average power below 5W.

The Mate 9’s average power is 3.1x higher than the Mate 8’s, but because peak performance goes up by the same amount, efficiency turns out to be equal. Qualcomm’s Adreno 530 GPU in Snapdragon 820/821 is easily the most efficient with this workload, and despite achieving about the same performance of Kirin 960, it uses less than half the power.

GFXBench T-Rex Offscreen Power Efficiency
(System Load Power)
  Mfc. Process FPS Avg. Power
LeEco Le Pro3 (Snapdragon 821) 14LPP 94.97 3.91 24.26 fps/W
Galaxy S7 (Snapdragon 820) 14LPP 90.59 4.18 21.67 fps/W
Galaxy S7 (Exynos 8890) 14LPP 87.00 4.70 18.51 fps/W
Xiaomi Mi5 Pro (Snapdragon 820) 14LPP 91.00 5.03 18.20 fps/W
Apple iPhone 6s Plus (A9) [OpenGL] 16FF+ 79.40 4.91 16.14 fps/W
Xiaomi Redmi Note 3
(Snapdragon 650)
28HPm 34.43 2.26 15.23 fps/W
Meizu PRO 5 (Exynos 7420) 14LPE 55.67 3.83 14.54 fps/W
Xiaomi Mi Note Pro
(Snapdragon 810 v2.1)
20Soc 57.60 4.40 13.11 fps/W
Nexus 6P (Snapdragon 810 v2.1) 20Soc 58.97 4.70 12.54 fps/W
Galaxy S6 (Exynos 7420) 14LPE 58.07 4.79 12.12 fps/W
Huawei Mate 8 (Kirin 950) 16FF+ 41.69 3.58 11.64 fps/W
Meizu PRO 6 (Helio X25) 20Soc 32.46 2.84 11.43 fps/W
Huawei P9 (Kirin 955) 16FF+ 40.42 3.68 10.98 fps/W
Huawei Mate 9 (Kirin 960) 16FFC 99.16 9.51 10.42 fps/W

Things only get worse for Kirin 960 in T-Rex, where average power increases to 9.51W and GPU efficiency drops to the lowest value of any device we’ve tested. As another comparison point, the Exynos 8890 in Samsung’s Galaxy S7, which uses a wider 12 core Mali-T880 GPU at up to 650MHz, averages 4.7W and is only 12% slower, making it 78% more efficient.

All of the flagship SoCs we’ve tested from Apple, Qualcomm, and Samsung manage to stay below a 5W ceiling in this test, and even then these SoCs are unable to sustain peak performance for very long before throttling back because of heat buildup. Ideally, we like to see phones remain below 4W in this test, and pushing above 5W just does not make any sense.

GFXBench Manhattan ES 3.1 / Metal Battery Life

The Kirin 960’s higher power consumption has a negative impact on the Mate 9’s battery life while gaming. It runs for 1 hour less than the Mate 8, a 22% reduction that would be more pronounced it the Mate 9 did not throttle back GPU frequency during the test. Ultimately, the Mate 9’s runtime is similar to other flagship phones (with smaller batteries), while providing similar or better performance. To reconcile Kirin 960’s high GPU power consumption with the Mate 9’s acceptable battery life in our gaming test, we need to look more closely at its behavior over the duration of the test.

GPU Thermal Stability

The Mate 9 only maintains peak performance for about 1 minute before reducing GPU frequency, dropping frame rate to 21fps after 8 minutes, a 38% reduction relative to the peak value. It reaches equilibrium after about 30 minutes, with frame rate hovering around 19fps, which is still better than the phones using Kirin 950/955 that peak at 11.5fps with sustained performance hovering between 9-11fps. It’s also as good as or better than phones using Qualcomm’s Snapdragon 820/821 SoCs. The Moto Z Force Droid, for example, can sustain a peak performance of almost 18fps for 12 minutes, gradually reaching a steady-state frame rate of 14.5fps, and the LeEco Pro 3 sustains 19fps after dropping from a peak value of 33fps.

In the lower chart, which shows how the Mate 9’s GPU frequency and power consumption change during the first 15 minutes of the gaming battery test, we can see that once GPU frequency drops to 533MHz, average power consumption drops below 4W, a sustainable value that still results in performance on par with other flagship SoCs after they’ve throttled back too. This suggests that Huawei/HiSilicon should have chosen a more sensible peak operating point for Kirin 960’s GPU of 650MHz to 700MHz. The only reason to push GPU frequency to 1037MHz (at least in a phone or tablet) is to make the device look better on a spec sheet and post higher peak scores in benchmarks.

Lowering GPU frequency would not improve Kirin 960’s low GPU efficiency, however. Because we do not have any other Mali-G71 examples at this time, we cannot say if this is indicative of ARM’s new GPU microarchitecture (I suspect not) or the result of HiSilicon’s implementation and process choice.

CPU Power Consumption and Thermal Stability Final Words
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  • nikhilmaurya10 - Friday, July 21, 2017 - link

    Believe me I bought the honor 8 pro with kirin 960 at 466 USD(india 30k RS), so they have achieved their goal of making a flagship level chip for below flagship price. After reading this review and finding that 8W power of that GPU i am worried about the VR content on this 2k display. One thing is good that this phone is huge metallic slab, that should keep it somewhat cool.
  • socalbigmike - Thursday, March 16, 2017 - link

    They ARE sponsored by Huawei.
  • Meteor2 - Wednesday, March 15, 2017 - link

    This. This is a great article but what's missing is the A10 (and Core M and Atom for comparison).

    I'm less interested in the deeper technical stuff, tbh. But I'm very interested in the performance, power consumption, and resulting efficiency. So I'd love to see this test battery for the A10 and Core too.

    Mind you, why don't you do SPi2000 and GB4 against power consumption, rather than only PCMark?
  • jjj - Tuesday, March 14, 2017 - link

    ARM was comparing A73 on 10nm vs A72 on 16nm in efficiency ,not peak power for both on same process.
    Likely the memory controller and the interconnect have an impact too in increasing the differences between the 950 and 960.
  • Matt Humrick - Tuesday, March 14, 2017 - link

    ARM's power comparison was for the same process and same frequency.
  • jjj - Tuesday, March 14, 2017 - link

    On a per same task basis not peak load.

    In this slide it's 10nm vs 16nm
  • degasus - Tuesday, March 14, 2017 - link

    > I cannot think of any CPU-centric workloads for a phone that would load two big cores for anywhere near this long

    You haven't run an emulator, have you? With a bit improved GPU drivers (here, EXT_buffer_storage), this will be a very good device for playing Gamecube and Wii games. This will stress two threads, and a bit the GPU.
  • tuxRoller - Friday, March 17, 2017 - link

    You're joking.
    Dolphin doesn't run on my pixel c at anything resembling a useful frame rate (even when it actually works).
  • MajGenRelativity - Tuesday, March 14, 2017 - link

    I'm not read up on all the lingo, but what does 16FFC stand for, and how does it differ from 16FF+?
  • Ian Cutress - Tuesday, March 14, 2017 - link

    Page 4:

    The Kirin 950 uses TSMC’s 16FF+ FinFET process, but HiSilicon switches to TSMC’s 16FFC FinFET process for the Kirin 960. The newer 16FFC process reduces manufacturing costs and die area to make it competitive in mid- to low-end markets, giving SoC vendors a migration path from 28nm. It also claims to reduce leakage and dynamic power by being able to run below 0.6V, making it suitable for wearable devices and IoT applications. Devices targeting price-sensitive markets, along with ultra low-power wearable devices, tend to run at lower frequencies, however, not 2.36GHz like Kirin 960. It’s possible that pushing the less performance-oriented 16FFC process, which targets lower voltages/frequencies, to higher frequencies that lay beyond its peak efficiency point may partially explain the higher power consumption relative to 16FF+.

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