Detailed Power Consumption Testing
When we started dissecting the power consumption concerns around the Radeon RX 480, that have since been mostly addressed by AMD with a driver fix and new control panel option, I knew this meant a much more strenuous power testing process going forward.
How do we do it? Simple in theory but surprisingly difficult in practice, we are intercepting the power being sent through the PCI Express bus as well as the ATX power connectors before they go to the graphics card and are directly measuring power draw with a 10 kHz DAQ (data acquisition) device. A huge thanks goes to Allyn for getting the setup up and running. We built a PCI Express bridge that is tapped to measure both 12V and 3.3V power and built some Corsair power cables that measure the 12V coming through those as well.
The result is data that looks like this.
What you are looking at here is the power measured from the GTX 1080. From time 0 to time 8 seconds or so, the system is idle, from 8 seconds to about 18 seconds Steam is starting up the title. From 18-26 seconds the game is at the menus, we load the game from 26-39 seconds and then we play through our benchmark run after that.
There are four lines drawn in the graph, the 12V and 3.3V results are from the PCI Express bus interface, while the one labeled PCIE is from the PCIE power connection from the power supply to the card. We have the ability to measure two power inputs there but because the GTX 1080 only uses a single 8-pin connector, there is only one shown here. Finally, the blue line is labeled total and is simply that: a total of the other measurements to get combined power draw and usage by the graphics card in question.
From this we can see a couple of interesting data points. First, the idle power of the GTX 1080 Founders Edition is only about 7.5 watts. Second, under a gaming load of Rise of the Tomb Raider, the card is pulling about 165-170 watts on average, though there are plenty of intermittent, spikes. Keep in mind we are sampling the power at 1000/s so this kind of behavior is more or less expected.
Different games and applications impose different loads on the GPU and can cause it to draw drastically different power. Even if a game runs slowly, it may not be drawing maximum power from the card if a certain system on the GPU (memory, shaders, ROPs) is bottlenecking other systems.
First, let’s look at our total power draw numbers.
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There are several interesting things to gleam from this data. First, we measure the power draw of the MSI RX 580 Gaming X card at 200 watts total. That is about 30 watts more than the Radeon RX 480 from ASUS that we measure at 170 watts of power draw. For this particular game, Rise of the Tomb Raider, we saw a 1-4% improvement in performance (though the 1% was at our tested 2560×1440 resolution). This comes a power penalty of 17%!
By contrast, the GTX 1060 6GB card from EVGA is 3-6% faster than the RX 580 yet shows only 115-120 watts of power being used! That gives us an 80 watt advantage in power consumption in favor of the GTX 1060 6GB card, a 66% difference! It would be a drastic understatement to say that this result shows Pascal as the superior GPU in terms of performance efficiency.
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In Witcher 3, the results are very similar. Based on our measurement the RX 580 pulls over 200 watts, the RX 480 uses 175 watts, and the GTX 1060 6GB uses 125 watts. If you are a user at all interested in temperatures, noise and thermals in your system, this is something worth noting.
As for the potential for overdraw from any single source of power, how does the power distribution break down between the motherboard slot and 8-pin/6-pin power connection with the RX 580 from MSI?
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Metro: Last Light represents one of our worst case scenarios and indicates the MSI RX 580 Gaming X 8GB card is using nearly 210 watts. Interestingly, only 40 watts of that is coming through the PCIe bus on the motherboard while the other 170 watts is being pushed through the 8-pin power connector from the power supply. While I realize that is over the 150 watt specification for those connections, modern power supplies are overbuilt to such a degree that this result doesn't really bother us. As we see more overclocked RX 580 cards hit the market though, it's worth keeping an eye on and monitoring how particular power supplies handle the strain.