AMD’s all-new RDNA 2 architecture for desktop computers has arrived via the RX 6000 line of graphics cards – a significant release, as it comes with full hardware support for the DirectX 12 Ultimate feature set, including the DXR API. Yes, ray tracing was now an integral part of AMD’s cutting-edge parts, and we wanted to see how effective Radeon’s display of the technology in the RX 6800 XT was – and how it compared to its closest competitor, the RTX 3080. Benchmarks showed Nvidia’s second-generation technology is faster than AMD’s first offering. But what’s the full story here?
To help put this piece together, XFX sent me a factory overclocking model of the RX 6800 XT, specifically the Speedster Merc 319 version of the card. Using its proprietary three-fan radiator design, this brutal card delivers booster clocks rated at 2340MHz, which is nearly five percent higher than the reference model, but I’ve seen it routinely reach hours in the 2400MHz range and beyond. While the XFX card is brand new, the design philosophy has much in common with the previous “THICC” range. The coolant is definitely the same, and it does a good job of keeping temperatures in the 70 ° C range under load. As I mentioned, it’s pretty brutal in terms of form factor. Sure in terms of sheer size, you need to make sure you have enough clearance in your case – they are around 34cm or 13.5in!
Regarding actual ray tracing metrics, it’s best to refer to the video here for full details of how to test individual RT effects and how well they handle them in each of our competing GPU architectures, but the main goal of this test was to isolate the individual stages of the RT pipeline to see how Nvidia is performing and AMD, and doing so in the context of three major RT effects: shadows, reflections, and global lighting.
Usually, in any RT scenario, there are four steps. First of all, the scene is prepared on the GPU, filled with all the objects that can affect ray tracing. In a second step, rays are fired at that scene, traversed and tested to see if they have collided with objects. Then there’s the next step, where the results from the second step are shaded – like the color of the reflection or whether the pixel is in or out of shadow. The final step is to reduce noise. As you can see, the GPU cannot send unlimited amounts of rays to be tracked – only a limited amount can be tracked, so the end result looks quite loud. Noise reduction smooths the image and creates the final effect.
Therefore, there are many factors that play a role in dealing with RT performance. Of the four steps, only the second is hardware acceleration – and the actual implementation between AMD and Nvidia is different, as GeForce cards contain additional hardware. RDNA 2 computes ray traversal on computation units, leading to competition for resources, while Nvidia does so in a specialized processor within RT core. The first setup stage may have significant CPU requirements, while the shadowing and noise reduction steps may have specific preferences for some GPU architectures. For example, Quake 2 RTX and Watch Dogs Legion both use a removal tool built by Nvidia and although it wasn’t designed to work poorly on AMD hardware (which Nvidia couldn’t access when coded), it’s definitely designed for It works best on RTX cards.
Regardless, in the video, I aim to be comprehensive in addressing the entire ray tracing pipeline on both architectures, while covering a range of effects. Ray tracing shadows are tested in Call of Duty: Black Ops Cold War (a title sponsored by Nvidia) as well as Dirt 5 (supported by AMD). I look at Ghostrunner’s ray-traced reflections in Unreal Engine 4, where I can examine the effect with a certain degree of adjustableability, and of course, Watch Dogs Legion’s reflections are also placed under the microscope. I chose this because AMD RT devices are used in controllers to deliver the effect, plus, by mod, I can access both the console and Nvidia denoisers. With global ray-tracked lighting, 4A Games’ impressive Metro Exodus is tested in depth, while I look at a more extreme example via the Quake 2 RTX tracked across the track – which now works on both AMD and Nvidia RT devices, thanks to the ultimate integration of Vulkan accessories RT.
So, what are the takeaways? I think there are some interesting findings here. Ray tracing shadows are generally inexpensive on resources on both the RX 6800 XT and RTX 3080 – the RTX 3080 sees minimal wins at the lower settings, which then increases as ray tracing quality increases at higher settings, in a game like Call of Duty black operations. For ray tracing reflections, the effect is more demanding on GPU hardware, but the visual win is more pronounced in many scenarios. The higher the randomness of reflected rays and the greater the amount of rays fired, the higher the performance of the RTX 3080 compared to the RX 6800 XT, resulting in approximately half the time in certain configurations. The RTX 3080’s efficiency feature diminished after a certain tipping point, and I’ve seen the same thing with global illumination: The RTX 3080 can deliver the effect in roughly half the time in a Metro Exodus, or up to a third of the time in a Quake 2 RTX, however, the amount of rays increases after that. Experienced that the RTX 3080 is less useful.
In general, it appears from these tests that the simpler the ray tracing, the more similar the effect width times are between competing structures. The Nvidia card is undoubtedly more capable across the entire RT pipeline, and the RTX 3080 appears to suffer fewer performance losses with the increased complexity of ray tracing, but at the less sophisticated end of the scale, AMD is competitive. Meanwhile, Spider-Man: Miles Morales from PlayStation 5 demonstrates that tracking Radeon rays can produce some surprising results on more challenging effects – using a significantly less powerful GPU than the 6800 XT. With that in mind, we need to accept that PC side ray tracing is still in its early days, especially when operating on AMD hardware. At the moment, I can only make general conclusions from a representative, but a small sample still. So far, we’ve only seen RT shades in AMD-sponsored titles, and I’m keen to see how future titles have evolved in collaboration with Team Red when claiming RT effects. While ray tracing has been with us now in the PC space for over two years, the story is only just beginning – and I can’t wait to see what happens next.
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