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Measuring Power Consumption: Let's Recap

AMD's Radeon HD 5000-Series: Measuring Power Efficiency
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What do these numbers tell us? First, the obvious: if you’re running an general-purpose application capable of utilizing your GPU, you aren’t going to load it down the same way you would if it were a game. This is why power measurement results in these scenarios don't yield the same elevated numbers seen in a more taxing benchmark like FurMark. As expected, they fall somewhere between idle and full load values we generally see in graphics cards reviews. But by how much? That naturally depends on the degree to which they utilize the GPU.

Here's a handy table with all the values from the various tests.


785Radeon 2900 XTRadeon HD 5670Radeon HD 5770Radeon HD 5870 1 GBRadeon HD 5870 2 GB
Crysis @ 1920x1080120
307
167
224
279
329
Adobe Photoshop CS4120
193
134
154
183
205
Cinebench R11 OpenGL Test132
232
175
202
220
253

*Peak Power Consumption in Watts

Of course, these applications don't just differ in GPU utilization, but also other resources as well (CPU, RAM, and hard disk), so those factors have to be taken into account, too. However, they affirm the claim that GPUs don't consume peak power numbers every time they're used.

The results above are quite interesting. Cinebench R11 actually pushes the processor more than Crysis. We can see this from the higher base system power consumption with Cinebench (121 vs. 132 W). Factor in that higher base system power consumption and you'll see that the actual power consumed by the graphics card is still lower in Cinebench than Crysis.

If we take out the base system's power consumption, the table above ends up more like the one below. Granted, there's some overlap in these numbers, since we do not know exactly how much power the integrated graphics consumes.


Radeon 2900 XTRadeon HD 5670Radeon HD 5770Radeon HD 5870 1 GBRadeon HD 5870 2 GB
Crysis @ 1920x1080187
47
104
159
229
Adobe Photoshop CS473
14
34
63
85
Cinebench R11 OpenGL Test100
43
70
88
121

*Peak Power Consumption attributed to each graphics cards in Watts

These numbers are important because they suggest the power draw we can realistically expect out of these cards when used in non-gaming/graphics applications. We now know just how much power is actually consumed, rather than just knowing it falls somewhere between idle and full load. We can also see the difference compared to the base system's power consumption. Should a graphics card with better power management comes along, we can point out the differences, and by just how much it improves.

Second, we've learned how managing power for different kinds of workloads really helps keep total power consumption under control. This can be seen from the PowerDVD results with the Radeon HD 5670. During H.264 playback, the Radeon HD 5670 hardly consumes more power than the integrated Radeon HD 3300, thanks to both processors’ UVD blocks. That's very efficient power management, which is even remarkable if we compare both chips side-by-side.

Another example can be seen in the Radeon HD 5870 1 GB. Running at UVD clocks (instead of full–speed) in PowerDirector allows the board to consume only 15 to 21 W more than the Radeon HD 5770. If it were to run at full speed, power consumption would be much higher.

Third, we were able to measure total power consumption. This kind of measurement can be done with similar applications, where the GPU is used to run a task completed in a certain amount of time. It’s useful in determining which graphics card offers the best performance and power consumption in that specific application. In this case, we were able to use PowerDirector. After testing, only 2 to 3 Wh separates the four Radeon HD 5000–series boards. That's quite an engineering feat.

The important element here is balance--a balance between performance and power consumption. The additional performance from the faster cards helps them finish the task and return to idle mode quickly. Overall consumption is still low enough so that we don't end up using significantly more power. It's doubtful we could possibly be aware of this just by looking at idle and full load power consumption numbers. In fact, this is the same type of comparison we like to make when looking at processors, but we’ve never really applied the same principles to graphics.

In more traditional graphics workloads, that same performance headroom benefits gamers who want higher frame rates or the ability to use slightly higher resolutions. Undoubtedly, you will be able to play Crysis at higher frame rates with the Radeon HD 5770 compared to the HD 5670. The same also applies to AMD’s Radeon HD 5870, which allows you to enjoy more demanding settings than the HD 5770.

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