Subject: General Tech | July 14, 2016 - 01:50 PM | Ryan Shrout
Tagged: video, Samsung, rx 480, radeon, Primochill, praxis, power consumption, podcast, phononic, gtx 1060, amd, 850 EVO, 4TB
PC Perspective Podcast #408 - 07/14/2016
Join us this week as we discuss a conclusion to the RX 480 power issue, the GTX 1060, a 4TB Samsung 850 EVO and more!
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Hosts: Ryan Shrout, Allyn Malventano, Jeremy Hellstrom, and Josh Walrath
Radeon Software 16.7.1 Adjustments
Last week we posted a story that looked at a problem found with the new AMD Radeon RX 480 graphics card’s power consumption. The short version of the issue was that AMD’s new Polaris 10-based reference card was drawing more power than its stated 150 watt TDP and that it was drawing more power through the motherboard PCI Express slot that the connection was rated for. And sometimes that added power draw was significant, both at stock settings and overclocked. Seeing current draw over a connection rated at just 5.5A peaking over 7A at stock settings raised an alarm (validly) and our initial report detailed the problem very specifically.
AMD responded initially that “everything was fine here” but the company eventually saw the writing on the wall and started to work on potential solutions. The Radeon RX 480 is a very important product for the future of Radeon graphics and this was a launch that needs to be as perfect as it can be. Though the risk to users’ hardware with the higher than expected current draw is muted somewhat by motherboard-based over-current protection, it’s crazy to think that AMD actually believed that was the ideal scenario. Depending on the “circuit breaker” in any system to save you when standards exists for exactly that purpose is nuts.
Today AMD has released a new driver, version 16.7.1, that actually introduces a pair of fixes for the problem. One of them is hard coded into the software and adjusts power draw from the different +12V sources (PCI Express slot and 6-pin connector) while the other is an optional flag in the software that is disabled by default.
Reconfiguring the power phase controller
The Radeon RX 480 uses a very common power controller (IR3567B) on its PCB to cycle through the 6 power phases providing electricity to the GPU itself. Allyn did some simple multimeter trace work to tell us which phases were connected to which sources and the result is seen below.
The power controller is responsible for pacing the power coming in from the PCI Express slot and the 6-pin power connection to the GPU, in phases. Phases 1-3 come in from the power supply via the 6-pin connection, while phases 4-6 source power from the motherboard directly. At launch, the RX 480 drew nearly identical amounts of power from both the PEG slot and the 6-pin connection, essentially giving each of the 6 phases at work equal time.
That might seem okay, but it’s far from the standard of what we have seen in the past. In no other case have we measured a graphics card drawing equal power from the PEG slot as from an external power connector on the card. (Obviously for cards without external power connections, that’s a different discussion.) In general, with other AMD and NVIDIA based graphics cards, the motherboard slot would provide no more than 50-60 watts of power, while any above that would come from the 6/8-pin connections on the card. In many cases I saw that power draw through the PEG slot was as low as 20-30 watts if the external power connections provided a lot of overage for the target TDP of the product.
Too much power to the people?
UPDATE (7/1/16): I have added a third page to this story that looks at the power consumption and power draw of the ASUS GeForce GTX 960 Strix card. This card was pointed out by many readers on our site and on reddit as having the same problem as the Radeon RX 480. As it turns out...not so much. Check it out!
UPDATE 2 (7/2/16): We have an official statement from AMD this morning.
As you know, we continuously tune our GPUs in order to maximize their performance within their given power envelopes and the speed of the memory interface, which in this case is an unprecedented 8Gbps for GDDR5. Recently, we identified select scenarios where the tuning of some RX 480 boards was not optimal. Fortunately, we can adjust the GPU's tuning via software in order to resolve this issue. We are already testing a driver that implements a fix, and we will provide an update to the community on our progress on Tuesday (July 5, 2016).
Honestly, that doesn't tell us much. And AMD appears to be deflecting slightly by using words like "some RX 480 boards". I don't believe this is limited to a subset of cards, or review samples only. AMD does indicate that the 8 Gbps memory on the 8GB variant might be partially to blame - which is an interesting correlation to test out later. The company does promise a fix for the problem via a driver update on Tuesday - we'll be sure to give that a test and see what changes are measured in both performance and in power consumption.
The launch of the AMD Radeon RX 480 has generally been considered a success. Our review of the new reference card shows impressive gains in architectural efficiency, improved positioning against NVIDIA’s competing parts in the same price range as well as VR-ready gaming performance starting at $199 for the 4GB model. AMD has every right to be proud of the new product and should have this lone position until the GeForce product line brings a Pascal card down into the same price category.
If you read carefully through my review, there was some interesting data that cropped up around the power consumption and delivery on the new RX 480. Looking at our power consumption numbers, measured directly from the card, not from the wall, it was using slightly more than the 150 watt TDP it was advertised as. This was done at 1920x1080 and tested in both Rise of the Tomb Raider and The Witcher 3.
When overclocked, the results were even higher, approaching the 200 watt mark in Rise of the Tomb Raider!
A portion of the review over at Tom’s Hardware produced similar results but detailed the power consumption from the motherboard PCI Express connection versus the power provided by the 6-pin PCIe power cable. There has been a considerable amount of discussion in the community about the amount of power the RX 480 draws through the motherboard, whether it is out of spec and what kind of impact it might have on the stability or life of the PC the RX 480 is installed in.
As it turns out, we have the ability to measure the exact same kind of data, albeit through a different method than Tom’s, and wanted to see if the result we saw broke down in the same way.
Our Testing Methods
This is a complex topic so it makes sense to detail the methodology of our advanced power testing capability up front.
How do we do it? Simple in theory but surprisingly difficult in practice, we are intercepting the power being sent through the PCI Express bus as well as the ATX power connectors before they go to the graphics card and are directly measuring power draw with a 10 kHz DAQ (data acquisition) device. A huge thanks goes to Allyn for getting the setup up and running. We built a PCI Express bridge that is tapped to measure both 12V and 3.3V power and built some Corsair power cables that measure the 12V coming through those as well.
The result is data that looks like this.
What you are looking at here is the power measured from the GTX 1080. From time 0 to time 8 seconds or so, the system is idle, from 8 seconds to about 18 seconds Steam is starting up the title. From 18-26 seconds the game is at the menus, we load the game from 26-39 seconds and then we play through our benchmark run after that.
There are four lines drawn in the graph, the 12V and 3.3V results are from the PCI Express bus interface, while the one labeled PCIE is from the PCIE power connection from the power supply to the card. We have the ability to measure two power inputs there but because the GTX 1080 only uses a single 8-pin connector, there is only one shown here. Finally, the blue line is labeled total and is simply that: a total of the other measurements to get combined power draw and usage by the graphics card in question.
From this we can see a couple of interesting data points. First, the idle power of the GTX 1080 Founders Edition is only about 7.5 watts. Second, under a gaming load of Rise of the Tomb Raider, the card is pulling about 165-170 watts on average, though there are plenty of intermittent, spikes. Keep in mind we are sampling the power at 1000/s so this kind of behavior is more or less expected.
Different games and applications impose different loads on the GPU and can cause it to draw drastically different power. Even if a game runs slowly, it may not be drawing maximum power from the card if a certain system on the GPU (memory, shaders, ROPs) is bottlenecking other systems.
One interesting note on our data compared to what Tom’s Hardware presents – we are using a second order low pass filter to smooth out the data to make it more readable and more indicative of how power draw is handled by the components on the PCB. Tom’s story reported “maximum” power draw at 300 watts for the RX 480 and while that is technically accurate, those figures represent instantaneous power draw. That is interesting data in some circumstances, and may actually indicate other potential issues with excessively noisy power circuitry, but to us, it makes more sense to sample data at a high rate (10 kHz) but to filter it and present it more readable way that better meshes with the continuous power delivery capabilities of the system.
Image source: E2E Texas Instruments
An example of instantaneous voltage spikes on power supply phase changes
Some gamers have expressed concern over that “maximum” power draw of 300 watts on the RX 480 that Tom’s Hardware reported. While that power measurement is technically accurate, it doesn’t represent the continuous power draw of the hardware. Instead, that measure is a result of a high frequency data acquisition system that may take a reading at the exact moment that a power phase on the card switches. Any DC switching power supply that is riding close to a certain power level is going to exceed that on the leading edges of phase switches for some minute amount of time. This is another reason why our low pass filter on power data can help represent real-world power consumption accurately. That doesn’t mean the spikes they measure are not a potential cause for concern, that’s just not what we are focused on with our testing.