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Does Undervolting Improve Radeon RX Vega 64's Efficiency?

Voltages, Frequencies & Power Consumption

Voltages & Frequencies

We already know that AMD's Radeon RX Vega 64 derives significant benefits from AVFS due to the telemetry’s efforts to keep things as balanced as possible. For instance, the graph below shows that the curves for two runs at the maximum power limit are almost exactly on top of each other. This is by design. However, the other three curves are a lot more interesting.

This is why we collected them in a second comparison graph of their own. Radeon RX Vega 64 and AVFS can make all the adjustments they want in Balanced mode.

Also, check out the two curves representing a manual 1.0V voltage setting. This is where things get weird. At its maximum power limit, RX Vega 64 does average 1V. However, at the default power limit, it overvolts significantly more than when it’s set to automatically control its voltages, and doesn’t manage to decrease them with changing load states as intricately as before. Consequently, not only does the effective voltage across our run end up well above the manually-set 1.0V, but also well above the Balanced mode’s effective voltage!

This behavior has a negative effect on the GPU’s frequency. It’s clear to see that our manual voltage setting without an increased power limit ends up being counterproductive; this combination effectively cancels the telemetry’s efforts. On the other hand, the same manual voltage setting, when combined with a maxed-out power limit, results in stable and usable clock rates. They're only slightly lower than those produced by the automatic setting, while consuming significantly less power.

Our test’s first conclusion is that manually undervolting Radeon RX Vega 64 without significantly raising its power limit is pointless once temperature is eliminated as an interfering factor. Manually lowering the power limit is the way to go instead. This can be accomplished through Power Save mode, for instance. Anything else is little more than urban legend.

Power Consumption

With this information in mind, we can turn our attention to power consumption. The first result to jump out is that AMD finally managed to minimize its idle power consumption. The 11W we observe is on par with Nvidia’s GeForce GTX 1080 Founders Edition. Already, AMD's card is in a much better place than when it launched.

Our bar graph confirms that manual undervolting using AMD's default power limit is pointless. It saves us less than 2W, but also results in a significantly lower frequency.

Undervolting with a maxed-out power limit yields the biggest positive surprise. The results tell us that undervolting, if you can even call it that, only makes sense close to the power limit's upper threshold. AMD’s reasons for the generous voltage increase probably come down to binning, which is to say that this trick should increase its yield rates.

Addendum: Power Consumption Curves

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All five power consumption curves appear in order of ascending magnitude.

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