I was reading Anandtech review of the power consumption of Nvidia shield tablet. While at first glance the GPU performance looked very impressive, the battery life data provided by the authors Joshua Ho and Andrei Frumusanu gives very good insights. Consider the battery life of Tab S 8.4 (using Exynos chipset with Mali graphics) and Shield Tablet running GFXbench 3.0. We can get the average power consumption as (Battery energy in WHr)/(Battery life in hours). They tested the shield tablet in two modes: Default (i.e. high performance) and capped performance. They reported observing GPU frequency of ~750MHz and ~450MHz in the two modes respectively. The battery life for the capped mode is inferred from the graph at about 14000 minutes (3.88 hours). For a very rough comparison, we will also compare with phablets such as Galaxy Note 3.
This gives us the following data:
1. Nvidia shield tablet (default, ~750MHz): 8.8W
2. Nvidia shield tablet (capped, ~450MHz): 5.09W
3. Tab S 8.4 (default): 5.5W
4. Galaxy Note 3: 3.1W
It is immediately obvious that in the default mode, shield tablet is consuming way too much power compared to Tab S. Given given the massive power consumption difference by reducing the GPU frequency, and the fact that the shield tablet gives good results for non-GPU bound tests , it is clear that most of the 9W of power is being consumed by the Tegra K1’s GPU.
The power consumption data is for the device, and hence includes the power consumption of components such as the screen and those can be very different across display types and sizes. We will only make very rough calculations here. To make very rough guesses, let us assume that the components other than the SoC and DRAM are consuming ~1.5W in the tablets and ~0.8W in the phone.
We get the following (VERY ROUGH) data for SoC + DRAM power consumption:
1. Tegra K1 (default, 750MHz): 7.3W
2. Tegra K1 (capped, 450MHz): 3.6W
3. Exynos 5420 (tablet): 4W
4. Snapdragon 800 (phone): 2.3W
Overall, I think it is quite reasonable to state that if Tegra K1’s stated GPU frequency targets of ~900MHz are not realizable in devices such as phones. I get the feeling that the Shield Tablet has been built more as a showcase device where the maximum GPU frequency has been set a bit too high in order to win benchmarks. I think if Tegra K1 ever ships in phones, it is likely that the GPU frequency will not exceed ~450MHz, and the GPU will not perform any better than it’s current mobile competitors. Perhaps Tegra K1 (particularly its GPU) is better suited in larger devices such as large tablets and ultraportable laptops where it can stretch it’s legs more.