Power Consumption, Overclocking & Undervolting
Power Consumption & Frequency across the Three Performance Modes
Before we get to our overclocking results, we’d like to provide a comparison of AMD's three power/performance profiles. From left to right, there’s the Power Saver mode with 212.8W, Balanced mode with 280.2W, and Turbo mode with 316.1W, as well as the corresponding clock rate curves.
The Power Saver and Balanced frequencies are fairly stable. However, things get really hectic once Turbo mode is activated; throttling due to to the power limit is clearly observable.
You might have noticed that these results are different from those of the air-cooled card in our launch article, since there are no flashy LEDs or fans to affect the outcome. The clock rates we measure are different as well.
Overclocking at the Maximum Power Limit
Even the updated version of AMD’s WattMan sent out the weekend before launch is buggy and unstable. Getting it to produce reliable and stable results took a lot of time and energy. AMD recommended setting the power limit to its maximum of +50%, so that’s exactly what we did.
And that's how you get to the 402.4W we measured through our extended benchmark run. This number comes close to AMD's 400W limit, which cannot be exceeded due to a factory-set cut-off. Tuning tricks do not work. Any supposed measurements exceeding that figure are definitely false.
Here’s the power consumption comparison bar graph:
So, what does a massive power consumption of 400W get you? Notwithstanding the unrealistic 1800 MHz we observe running AutoCAD 3D without generating a true 3D load, not a whole lot. Stable averages attained running actual games for 30 minutes don’t show large performance gains if the amount of power needed to get there is taken into account.
All of this means that we either received an inferior sample, or other reviewers received golden samples. Or maybe they just used the outdated and buggy drivers we discussed in the introduction. In addition, WattMan’s still unable to provide usable data for small overclocking gradations. The top two dynamic power management (DPM) state values of the manual frequency and voltage settings are faulty and lead to unexpected behavior, which can go as far as system crashes. Increasing the clock rate via the percentage setting was the only way to make overclocking work at all.
Unigine Heaven stabilized just shy of a respectable 1.7 GHz running at 1920x1080 and its lowest quality settings. Doom at Ultra HD only made it to 1673 MHz. Our “stability test,” The Witcher 3, threw in the towel once we tried to exceed 1.6 GHz.
All of these results, taken together, indicate that power consumption is the limiting factor.
Frequency vs. Gaming Performance
Depending on the game, AMD’s Radeon RX Vega 64 can be overclocked by 12 to 18 percent before crashes start occurring. This is why we ran different games using both the Balanced mode used for our launch article and the maximum possible overclock capable of short-term stability. We skipped the long-term stability tests for all games except for The Witcher 3 and Doom due to time considerations. The benchmark results show that our previous conclusions weren’t that far off.
Doom’s meager 12% performance boost (in exchange for an 18% frequency increase) doesn't represent great scaling. The same can be said for The Witcher 3’s 7%-higher performance that’s achieved by increasing the clock rate by 11%. Allow it to sink in that you pay for those 7% with a 44% (or 120W) power consumption increase, and you'll realize how ludicrous the situation is.
It’s certainly possible to overclock the Radeon RX Vega 64, but doing so doesn't make much sense. Games that didn’t run well before aren’t going to suddenly become (more) playable after overclocking the card.
How about Undervolting?
Undervolting worked well for Hawaii, Fiji, and Polaris. However, with the current software, it doesn't really provide any added value for Vega. Manually lowering the voltages for the two top frequency settings results in either crashes or a much-reduced clock rate. As a result, we cannot corroborate rumors that undervolting increases Radeon RX Vega 64’s overclocking potential.
Unfortunately, we only have one sample, so it's hard to tell if we're limited by a poor example of Vega 10, incomplete software, or honest reporting where others are sugar-coating this situation. There's no point in making things up to generate headlines, though. Truth, uh, finds a way. We can’t even compare our results to the Vega Frontier Edition because AMD's latest driver for Radeon RX Vega 64 completely disables gaming mode, and with it WattMan, for the Frontier Edition card.
Cooling at 400W Power Consumption & Maximum Overclock
Now the question is how to get rid of 400W of waste heat. After 30 minutes of running The Witcher 3, our measured GPU temperature levels off at 52°C.
This is a good result for an all-in-one liquid cooler with a relatively small 240mm radiator. It doesn’t really get much better.
If you're a fan of quieter acoustics or cooler temperatures, you'll need to find a viable 360mm or 480mm radiator. In that case, the CPU could be included in the loop as well.
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