AMD’s brand new RDNA 2 architecture has arrived for desktops via the RX 6000 series of graphics cards – and this is a key version that brings full hardware support for the DirectX 12 Ultimate feature set, including the DXR API. Yes, ray tracing is now part of AMD’s high-end components, and we wanted to know how effective the Radeon version of the technology is in the RX 6800 XT – and how it compares to its closest competitor, the RTX 3080. showed that Nvidia’s second generation technology is faster than AMD’s debut offering, but what’s the full story here?
To put this piece together, XFX sent me an example of the RX 6800 XT at the factory, specifically the Speedster Merc 319 edition of the card. Using its own three-fan cooler design, this monstrous card delivers a boost clock of 2340MHz, about five percent higher than the reference model, but I have seen it regularly reach 2400MHz and beyond. While the XFX card has a brand new design, the design philosophy has much in common with its previous ‘THICC’ series. The cooler is definitely similar and does a great job of keeping the temperature at the low 70s Celsius range under load. As I did mention, it is somewhat animalistic in terms of form factor. Sure, in terms of the large amount, you need to make sure you have enough clearance in your case – it’s about 34 cm or 13.5 inches long!
In terms of actual beam tracking statistics, it’s best to refer to the video here for a full breakdown of how I tested individual RT effects and how well they handle on each of our competing GPU architectures, but the main purpose of this test was to isolate individual stages of the RT pipeline to see how Nvidia and AMD are performing, and to do so within the context of three key RT effects: shadows, reflections, and global lighting.
Thanks to XFX for sending Alex the RX 6800 XT Speedster Merc 319 version of the card that made this content possible.
In any RT scenario, there are usually four steps. To begin with, the scene is prepared on the GPU, filled with all the objects that can affect ray detection. In the second step, rays are fired at the scene, traversed and tested to see if it hits objects. Then there is the next step, where the results of step two are overshadowed – such as the color of a reflection or whether a pixel is in or out of the shadow. The last step is denial. You see, the GPU cannot emit unlimited amounts of rays to be detected – only a limited amount can be detected, so the end result seems rather noisy. Denoising makes the image smoother and delivers the final effect.
Thus, there are numerous factors that play into dealing with RT performance. Of the four steps, only the second hardware was accelerated – and the actual implementation between AMD and Nvidia is different, with GeForce cards having additional hardware. RDNA 2 calculates beam passage on the computing units, which provides competition for resources, while Nvidia does this in a specialized processor within the RT core. The initial setup stage may have important CPU requirements, while the shading and denoising steps may have specific preferences for certain GPU architectures. For example, Quake 2 RTX and Watch Dogs Legion use a denoiser built by Nvidia, and although not designed to work badly on AMD hardware (which Nvidia would not have had access to when they coded it), it definitely designed to run as well as possible on RTX cards.
Either way, in the video I want to be comprehensive in addressing the entire pipeline for beam detection on both architectures and covering a variety of effects. Shadows followed by Ray are tested in Call of Duty: Black Ops Cold War (a title sponsored by Nvidia) as well as Dirt 5 (supported by AMD). I watch radiation track reflections in Ghostrunner in Unreal Engine 4, where I can examine the effect with some adaptability, and Watch Dogs Legion’s reflections are of course also examined. I chose this because AMD RT hardware is used in the consoles to deliver the effect, and via modding I can access both console and Nvidia denos. With the global illumination of the rays, the incredible Metro Exodus from 4A Games is being tested in depth, while I look at a more extreme example through the groundbreaking Quake 2 RTX – which now works on both AMD and Nvidia RT hardware, thanks to the integration of the finalized Vulkan RT extensions.
The Digital Foundry overview of the BIG NAVI cards and how they are put together in more general terms compared to their Nvidia counterparts.
So, what’s the takeaway? I think here are some interesting results. Shadows in the rays are generally cheap for RX 6800 XT and RTX 3080 – with the RTX 3080 minimal gains at lower settings, which then increase as the radiation detection quality increases at higher settings, in a game like Call of Duty. Black Ops. For reflections detected by the rays, the effect is much more demanding on GPU hardware, but the visual victory is more pronounced in many scenarios. The greater the randomness of the reflected rays and the greater the amount of rays fired, the greater the risk of the RTX 3080 compared to the RX 6800 XT, which in some configurations delivers almost half the time. However, the efficiency advantage of the RTX 3080 has diminished after a certain tipping point, and I have seen the same with global relief: the RTX 3080 can deliver the effect in Metro Exodus almost half the time, or even a third of the time in Quake 2 RTX, but still increasing the amount of rays after this, the RTX 3080 had less advantage.
In general, it seems from these tests the simpler the radiation detection, the more the version times for the effect between the competing architectures. The Nvidia card is undoubtedly more capable across the entire RT pipeline, and the RTX 3080 seems to have less dramatic performance losses as the complexity of ray traces increases, but at the less complex end of the scale, AMD is competitive. Meanwhile, PlayStation 5’s Spider-Man: Miles Morales shows that Radeon Beam Tracking can deliver impressive results on more challenging effects – and that it uses a GPU that is significantly less powerful than the 6800 XT. And with that in mind, we have to assume that ray tracing on the PC side is still in its early days, especially when used on AMD hardware. At the moment I can only draw general conclusions from a representative but still small example. So far, we’ve only seen RT shadows in AMD-sponsored titles, and I’m eager to see future titles evolve in collaboration with Team Red for demanding RT effects. While ray tracing has been with us in the computer space for over two years, the story is just beginning – and I can not wait to see what comes next.