While AMD’s RX 480 GPU has been generally well-received, reviewers from several sites picked up a power consumption issue after the card debuted last week. Specifically, the RX 480’s 8GB configuration with 8Gbps GDDR5 exceeds the maximum amount of power it should draw from the PCI Express slot according to the PCI Express specification.
Tom’s Hardware broke the initial story and has since conducted an exhaustive retest and characterization of the problem. Over the weekend, AMD contacted reviewers to inform them that it would have a response ready by Tuesday evening. We’re going to dive into that response, but let’s first take a look at what the problem is. As far as we’re aware, this issue affects both the 4GB and 8GB variants of the RX 480.
Modern GPUs draw power from two sources — the PCI Express slot itself, and one or more PCI Express connectors attached to the back of the card. These auxiliary connectors typically provide the bulk of a high-end GPUs power, since the PCI Express slot itself can only provide a limited amount of current.
Most of the time, when we talk about GPU power requirements, we talk about them in terms of wattage. As THG’s follow-up article notes, however, this is fundamentally inaccurate. The issue at hand is how much current is being drawn. Testing from multiple sites has demonstrated that the RX 480 draws too much of its current across the PCI Express slot. While the card’s average current draw conforms to spec, it can spike as high as 6.74 amps, which is well outside the limit set by the PCI-SIG (that’s the Peripheral Component Interconnect Special Interest Group).
THG goes on to note, however, that while this issue has gotten a fair bit of play in the media and kicked off a great deal of speculation, “we don’t think this is such a big deal.” They go on to note that at some point, the latest graphics cards began dedicating additional pins on the card to provide 12V power, though the amount of allowed current did not change.
THG’s view, which we agree with, is that while this issue is definitely something AMD should address, it is not a threat to the vast majority of properly-built motherboards and systems. Nonetheless, not all motherboards are well made, and some users could attempt to overclock their hardware, exacerbating the situation further.
Last night, AMD sent over the following statement:
We promised an update today (July 5, 2016) following concerns around the Radeon RX 480 drawing excess current from the PCIe bus. Although we are confident that the levels of reported power draws by the Radeon RX 480 do not pose a risk of damage to motherboards or other PC components based on expected usage, we are serious about addressing this topic and allaying outstanding concerns. Towards that end, we assembled a worldwide team this past weekend to investigate and develop a driver update to improve the power draw. We’re pleased to report that this driver—Radeon Software 16.7.1—is now undergoing final testing and will be released to the public in the next 48 hours.
In this driver we’ve implemented a change to address power distribution on the Radeon RX 480 – this change will lower current drawn from the PCIe bus.
Separately, we’ve also included an option to reduce total power with minimal performance impact. Users will find this as the “compatibility” UI toggle in the Global Settings menu of Radeon Settings. This toggle is “off” by default.
Finally, we’ve implemented a collection of performance improvements for the Polaris architecture that yield performance uplifts in popular game titles of up to 3%. These optimizations are designed to improve the performance of the Radeon RX 480, and should substantially offset the performance impact for users who choose to activate the “compatibility” toggle.
AMD is committed to delivering high quality and high performance products, and we’ll continue to provide users with more control over their product’s performance and efficiency. We appreciate all the feedback so far, and we’ll continue to bring further performance and performance/W optimizations to the Radeon RX 480.
That 48-hour deadline means we should see an updated driver by Thursday evening, at which point we will test the performance impact of the changes. While we can’t duplicate the same level of power supply testing, we’ll also measure total system power consumption for any changes.
The driver is expected to improve power draw by shifting how current is pulled over the 6-pin PCI Express connector. While this risks putting the 6-pin connector out of spec, the vast majority of power supplies are more than capable of providing the current required to run the GPU in this configuration. Users that aren’t satisfied with this option, or that encounter any sort of issue, will be able to check a “Compatibility” mode that will presumably modify GPU frequency to ensure the card never exceeds power draw, even transiently. Given that the card’s average current draw is within PCI Express specs according to THG, this should have a minimal impact on overall performance. We’ve already seen how relatively small changes to operating frequency can have a dramatic impact on power consumption (the R9 Nano is Exhibit A for this trend).
We were aware of this issue before our RX 480 review went to print, but intended to test and cover the fix in a separate article rather than stuffing more verbiage into a review already edging up on 4,000 words [Oh come on, Joel, you were just getting started! -Ed]. Once AMD releases its new driver, we’ll put the card through a new round of testing and report our findings. Tests from other sites indicate that the RX 480’s voltage is bumping up against its maximum power settings at default; Legit Reviews saw a notable performance improvement from undervolting its card, even without touching base clock speed.