The best graphics cards need to compete not just on performance and price, but also on features. Now that the RX 6900 XT, RX 6800 XT, and RX 6800 are joining Nvidia in supporting ray tracing via hardware, we really want to know how they compare in performance. Who will take top honors in our GPU benchmarks hierarchy, and how will things change if we test with ray tracing enabled?
There have been various hot takes on ray tracing in games over the years. I remember when Quake 4 Enemy Territory got a prototype ray tracing mod back in 2008. It looked pretty cool, but performance was terrible. 720p at 16 fps on a 16-core CPU? But at least it was something!
Flash forward a decade and Nvidia's RTX hardware promised far superior quality and performance. Except, even with RTX cards, games are still using a hybrid rendering approach where most of the rendering is done using traditional methods, and ray tracing is only applied after the fact for a few specific effects like reflections or shadows.
What would it take to do full path tracing on a game, using today's modern GPUs that support ray tracing calculations? Quake II RTX and Minecraft RTX sort of already do this, but they're older and less complex games with path tracing tacked on. Now UL has added a feature test for 3DMark that does a fully ray traced rendering of assets from the Port Royal benchmark. (Note that you'll need the Advanced or Pro version to access the DirectX Raytracing Feature Test, as it's called.)
We like the idea of being able to compare 'pure' ray tracing performance on the various GPUs. The 3DMark DXR Feature Test now gives us another way to do that, and while it doesn't report the number of ray/triangle intersections per second (which is what we'd really like to see), it does provide an fps score that's directly correlated with the ray tracing hardware. We've rounded up the current RTX GPUs as a point of reference below. More important will be seeing how AMD's upcoming Big Navi stacks up, with the RX 6900 XT, RX 6800 XT, and RX 6800 all set to launch in the next month or so.
We ran all the RTX cards through the DXR Feature Test, with the exception of the RTX 2070 and 2080 (those should land about midway between the newer Super variants). The GeForce RTX 3090 is over 4X the performance of the RTX 2060, the RTX 2080 Ti is a bit more than twice as fast as the 2060, and the GeForce RTX 3070 is slightly faster than the 2080 Ti. The RTX 3090 is also 19 percent faster than the GeForce RTX 3080, which is a bigger gap than in most of the games we've tested. Basically, things are far more GPU limited here, so theoretical performance ends up pretty close to reality.
How close? We crunched some numbers, using the number of RT cores, the GPU clocks, and the RT core generation. Nvidia says the second gen 30-series RT cores are about 70 percent faster than the first gen 20-series RT cores. That means the 3070 for example should be about 7 percent faster than the 2080 Ti FE, while the 2080 Ti should be 150 percent faster than the RTX 2060.
The 30-series GPUs scale almost perfectly in line with expectations. 3070 is indeed 7 percent faster than 2080 Ti, 3080 is 48 percent faster than 3070 (47 percent expected), and 3090 is 19 percent faster than 3080 (vs 19.5 percent expected).
The results on the 20-series parts end up being more varied, however. The 2060 Super is 14 percent faster than the 2060 (vs 11 percent expected). However, the 2070 Super is only 35 percent faster than the 2060 (41 percent theoretical), 2080 Super is 65 percent faster (73 percent theoretical), and the 2080 Ti is 127 percent faster (vs. 150 percent theoretical). Still, that's mostly close enough to the respected behavior and a good starting point.
We wanted to run the DXR Feature Test on some non-RTX GPUs as well, but it basically laughed at us and mocked our hardware. "Your puny GTX 1660 Super and GTX 1080 Ti can't handle the ray traced truth!" Actually, it told us that our hardware didn't support the required DXR Tier 1.1 feature set needed to run the test. So much for DXR on GTX via drivers and shader hacks: Ray tracing hardware acceleration is required.
The bigger question: How will AMD's RX 6800, RX 6800 XT, and RX 6900 XT fare against RTX 3070, RTX 3080, and RTX 3090? Based on theoretical estimates, the 6900 XT may land about midway between the 3070 and 3080, while the 6800 XT would be just a bit faster than the 3070, with the RX 6800 sitting between the 2080 Ti and 2080 Super. But theoretical performance estimates may not match reality, and we're definitely interested to see how things shape up later this month.
There's a lot more to discuss with the 3DMark DXR Feature Test. For example, the way it runs isn't quite what we expected. The default settings render with 12 randomized samples per pixel at 1440p, and like most path tracing algorithms, the inputs from those samples are combined to give a final pixel color result. Then things are sampled again and the quality of the result improves. Normally, this process would be repeated until some desired quality level is achieved.
The catch is that 3DMark DXR Feature Test does all of the sampling and accumulation in real-time. The sample count specifies the rate of accumulation, and directly impacts image quality when things are in motion. However, once the camera stops moving, you end up with a similar maximum quality result for each scene (after the same amount of total time).
With a 2-sample setting, when the camera starts moving things look quite grainy compared to the 12-sample default, which in turn looks slightly worse than the maximum 20-sample setting. Once the camera pauses for a few seconds, however, the on-screen results start to converge quite quickly. Check out these image quality comparisons.
The above gallery shows images of the same scene right after the camera pauses, up until just before it starts moving again. The first three "start" images are thus the 'worst' quality, while the three "end" images are the 'best' quality. Note that the screengrabs are taken from video captures made with ShadowPlay, so there are some compression artifacts that you should ignore. This was to make capturing the same frame for each setting easier. (These results are from an RTX 2080 Ti.)
The video compression artifacts obfuscate a lot of the additional noise you'll see when a scene is in motion, particularly on the 2-sample setting. However, check out how similar the images look given even a small amount of time for an image to stabilize. The three 'end' results are all basically the same, with the only difference being how the randomized sampling plays out. The biggest factor by far, however, is performance.
Using an RTX 2080 Ti, the average performance for the default 12 samples is 30.2 fps. Dropping down to two samples per pixel, performance jumps to 165 fps, while increasing the sample count to 20 samples per pixel cuts performance to just 18.1 fps. In other words, the number of samples per pixel per frame directly impacts performance, almost linearly.
What I want to see is a deep learning derived denoising algorithm running on top of the various sample counts. Sure, the 2-sample image quality is quite noisy by default, but then so is Quake II RTX. Look at the following as an example:
The 'noisy' image runs 15-25 percent faster, but it's far more useful if you're actually trying to make a playable game. The goal then is to do enough samples to get an image that can be converted into a nicer looking result. Think DLSS, but instead of upcsaling it would remove noise and interpolate between the various pixels in a consistent fashion.
The number of randomized samples per pixel required to get a near-perfect path tracing result is typically in the hundreds. That's not going to happen any time soon for real-time gaming applications. However, Quake II RTX allows you to adjust the number of samples it uses for the photo mode, ranging from 100 up to 8000.
The maximum takes about a minute to render a single frame at 1080p, while 100 samples can be done quite quickly. The image quality meanwhile doesn't change much beyond the baseline 100 samples, though it would probably matter more if you had a more complex game to render than Quake II.
The choice is more samples, lower performance, and higher image quality; or fewer samples, better performance, and lower image quality. Finding a good balance between quality and performance is all we need for games to make use of higher quality ray traced rendering techniques. Outside of the photo mode, Quake II RTX uses only a few samples per pixel and can easily reach playable performance on RTX graphics cards.
Of course, there's are several remaining questions. First, for denoising, would it require Nvidia's Tensor cores, or could it be done via FP16 on regular GPU shaders (making it compatible with AMD GPUs)? And how much would it impact performance?
More important is the question of whether fully ray traced games or graphics even matter. Current ray tracing games typically use a hybrid rendering approach, with rasterization handling most of the underlying graphics, and ray tracing effects only used for things like reflections, shadows, or global illumination. But if hybrid rendering can achieve the same visual result while running substantially faster, isn't that the best overall result?
One concern is that hybrid rendering requires all the code for traditional rasterization, plus code for ray tracing, and that means potentially more work for the game developers. Then again, with support for ray tracing built into Unreal Engine and Unity, that's less of a problem than you might thing. Regardless, we're not likely to leave rasterization behind any time soon.