Today AMD released its 16.7.1 Radeon Software Crimson driver with specific fixes for the Radeon RX 480’s PCI-E power consumption issue. This issue has been floating around since the first RX 480 reviews were released last week. Essentially the RX 480, in its stock form, draws more than 75 Watts of power through the motherboard’s PCI-E x16 slot. The majority of graphics card on the market do not do this. 75 Watts is the limit set by the PCI-E specification but there’s a lot of disagreement in the community around whether or not overdrawing power from this source is genuinely dangerous for the health of motherboard.
AMD is addressing these power consumption concerns by offering a new toggle in its driver that enables ‘Compatibility Mode’. This setting limits the amount of power the RX 480 pulls through the PCI-E slot to 75 Watts. This toggle is disabled by default in AMD’s drivers so if you are concerned about this issue you’ll need to enable this option manually. In the driver’s release notes AMD’s stated that with compatibility mode enabled the RX 480 takes a slight performance hit. The company also claims that it has improved the RX 480’s performance in this update by 3% which, “should substantially offset the performance impact…” of enabling compatibility mode.
With the immediate issue resolved the question still remains: how could AMD allow this to occur? AMD’s been producing PCI-E compliant graphics cards for years. The RX 480 passed AMD’s internal PCI-E compliance testing. If AMD knew they were going to be bumping right up against the RX 480’s 150 Watt TDP why didn’t they chose an 8-pin PCI-E connector rather than a 6-pin? These are the questions that cast the future success of AMD’s Radeon Technologies Group into doubt.
Coming back to the issue at hand, let’s investigate the impact of the 16.7.1 driver on the performance and power consumption of AMD’s RX 480. We’ll be testing on the same FX-8370 based system we used in our initial RX 480 review and the follow-up piece on thermal throttling and PowerTune limits.
Looking directly at power consumption in our Total War: Warhammer DirectX 12 benchmark we can see the impact of AMD’s Power Efficiency toggle in the middle spike and the compatibility mode is the spike on the right. Compatibility mode very clearly reduces the power consumption of the RX 480. But how is it saving ~15 Watts of power compared to the stock RX 480?
In its stock form the RX 480 is pegged in its 1266Mhz boost state for the entirety of our Warhammer benchmark.
With the Power Efficiency Toggle enabled we see slight dips below the 1266Mhz boost clock.
With compatibility mode enabled we see even bigger clock speed dips and variance from the top boost clock state. Thus it would appear that AMD’s reduced power consumption by forcing the RX 480 to throttle more often when compatibility mode is enabled.
Looking at raw performance we can see that the RX 480 take a 1 percent average frame rate hit from enabling its Power Efficiency toggle and a 2 percent hit from enabling compatibility mode. In the real world the 1 FPS difference between stock and compatibility mode is imperceptible.
The slight upside to enabling compatibility mode is marginally better performance per watt. It’s not going to put Polaris on even footing with Pascal in terms of efficiency but it’s nice to have some kind of silver-lining to this mess.
With the Radeon Software 16.7.1 driver AMD has atoned for its sins against the PCI-E slot. Compatibility mode does exactly what AMD promised. While it’s troubling that this was an issue at all; AMD’s response was adequate in my view.
AMD’s RX 480 reference design had a lot of good things going for it. But its clear that the company missed the mark on power consumption, thermal headroom, and honestly length too. If Nvidia’s is getting one thing right it’s that building the best reference design that money can buy is a worth while investment even if that means putting pressure on the AIBs. Gamers want small, power efficient, quiet, cool, and attractive looking graphics cards that overclock to the moon. Four of these six issues can be home runs without any investment in silicon or IP and imperfection in any of these categories is considered a failure by the community.
These challenges aside, it’s hard not to get a little excited about the custom RX 480 designs that AMD’s partners will begin rolling out later this month. It’ll be fun to see if AMD can blunt Nvidia’s GTX 1060 flavored assault.S|A