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AMD’s Radeon RX 6800 XT is a winner

AMD’s new AIB is speedy and powerful—and there’s more to come

Posted: By Jon Peddie & Robert Dow 11.18.20

AMD has announced its new line of Radeon boards based on the Navi 21 GPU architecture. We have heard rumors and hints from AMD about “Big”-Navi for over a year. Our first examination of the new AIB indicates it was worth the wait.

AMD hasn’t been a contender in the high-end for a while. As a result, Nvidia has enjoyed the enthusiast space to itself. Perhaps, now Nvidia has some serious competition. Not only is the new Radeon RX 6800 XT a powerful competitor, AMD itself is a much stronger company. As such, it is now capable of mounting a robust marketing program to back up the product. That is an element that has been missing in the past.

The heart of the Navi 21 is AMD’s RDNA 2. It, says AMD, introduces significant architecture advancements from previous RDNA architecture. It has an enhanced compute unit, a new visual pipeline with Ray Accelerators. The company claims up to 1.54x higher performance-per-watt on a variety of games they tested. Also, RDNA 2 offers a 1.3x higher frequency at the same per-CU power compared to an RX 5700 XT. The RDNA 2 provides DirectX ray-tracing (DXR), variable rate shading (VRS), and AMD’s FidelityFX capabilities as well.

AMD is incredibly proud of the new Infinity Cache. AMD says they focused on delivering breakthrough speeds with power efficiency in RDNA 2. The on-die cache results in frame data with much lower energy per bit says AMD. The 128MB Infinity Cache provides up to 3.25x effective bandwidth of 256-bit of GDDR6, says AMD. And when adding power to the equation, it achieves up to 2.4x more effective bandwidth/watt vs. 256-bit GDDR6.

New to the AMD RDNA 2 compute unit is the implementation of the Ray Accelerator. Ray Accelerators, says AMD, provides a massive acceleration for intersecting rays.

AMD’s RX 6800 XT has 72 Ray-Accelerator units (Source: AMD)

 

 

Each Ray Accelerator can calculate up to four rays per bounding box intersections or one ray per triangle intersection with every clock. The Ray Accelerators calculate the intersections of the rays with the scene geometry in a bounding volume hierarchy. Then it sorts them and returns the information to the shaders for further scene traversal or result shading.

Variable-rate shading (VRS) adjusts the shading rate for different regions of an image. VRS was initially developed for gaze tracking in VR HMDs for foveated rendering. It allows the GPU to concentrate the rendering work where it is most needed. VRS applies higher shading to the most complex parts of the image. These areas usually have the most important visual cues in an image. Nvidia introduced the concept in their Turning architecture.

 AMD says their RDNA 2 VRS functionality is throughout the entire pixel pipe and offers shading rates of 1 x 1, 2 x 1, 1 x 2, and 2 x 2.

The RDNA 2 VRS provides a unique shading rate to every 8 x 8 region of pixels. That granularity enables developers to make appropriate decisions about the shading rate for a given region.

The RX 6800 XT includes the Radeon Media Engine. It offers hardware-accelerated encode/decode capabilities. The engine supports popular codecs such as H.264, H.265, VP9 (decode only), and AV1 (decode only).

The ATI Rage series was the first 3D graphics accelerator developed by ATI that AMD acquired back in 2006. The Rage 3D graphics chip ushered in a new era of PC gaming. To celebrate that milestone and as a precursor to AMD’s Radeon brand, the company introduced a new Rage Mode for the Radeon RX 6800 XT AIBs.

Rage Mode is one of three, one-click, performance-tuning presets available on the Radeon RX 6800 XT, along with Quiet and Balanced. These pre-sets automatically adjust power and fan levels to allow quick and easy customization of the GPU’s behavior.

On the backplate, the outputs include an HDMI 2.1 with variable refresh rate (VRR) capability. There are two DisplayPort 1.4a connectors. And there is a USB Type-C connector for VR headsets or FreeSync monitors. USB-C supports Display alt mode and display compression supporting daisy-chaining if the monitor supports it.

There are two versions of the RDNA 2-based Radeon RX 6800 and the forthcoming RX 6900 XT version.

 

AMD’s Radeon series AIBs (Source: AMD)

 

The Radeon6800 and 6800XT are available now, and the RX 6900 XT will be available on 8 December.

A testing we will go ...

We ran the Radeon RX 6800 XT through the usual series of tests and compared it to an Nvidia RTX 3080, 3970, and a Radeon 5700 XT on an AMD and an Intel platform. We used Metro Exodus Ultra, Wolfenstein River FSAA, Wolfenstein Lab FSAA, SOTTR 4K Ultra SMAA2X, Time Spy, Time Spy Extreme, Port Royal, Crytek Noir, WatchDog - Legion 4K Very High, and 1440p Very High for testing. We didn’t test the anti-lag. For reference, the prices of the AIBs are:

  RX 6800 XT 5700 XT RTX 3070 RTX 3080
Price 649 399 500 700
Power 300 225 200 320

 

Comparison of Pmark scores for three AIBs on two platforms

 

“To my surprise, said Robert Dow, “ the RX 6800 XT is equal to the GeForce 3080. In traditional performance, the FPS at 4K with high to very high presets, the two cards are virtually identical in FPS. The RTX 3080 does outperform the RX 6800XT when it comes to ray-tracing, and I think that was to be expected.“

 

Comparison of average fps for three AIBs on two platforms

 

In our tests, the RX 6800 XT outperformed the RTX 3080 overall, but much of that was due to the Wolfenstein scores, which was the outlier. When removed from the overall average, the FPS rates were virtually identical for both AIBs. 

Comparison of average test scores for three AIBs on two platforms

 

The same could be said for the synthetic benchmarks. The high-end RTX outperformed the RX 6800 XT overall, but when you toss out Crytek Noir (a test in which the RTX 3080 held a significant advantage), the synthetic scores were almost identical, with the RTX having a slight edge.

All three AIBs performed better on the Ryzen 9 3900X than the 10th Gen Core i9. With the RTX 3070 holding the Pmark edge on both platforms.

AMD’s Radeon RX 6x00 product line (Source: AMD)

 

Last generation comparison

AMD has used the X 5700 XT as a comparative device to evaluate the XT 6800 XT. We thought we should do the same to see if the comparisons AMD made were similar. We wouldn’t expect them to be exact to what we discovered ssine w cannot perfectly replicate their test setup.

Comparison of average fps for two generations of AMD AIBs

 

The tests were run on both platforms.

Comparison of average test scores for two generations of AMD AIBs

 

As the charts below show, the Radeon RX 6800 XT delivered a higher frame rate than the bar X 5700 XT and got a higher benchmark score. This doesn’t quite match AMD’s claims, but it is still a substantial improvement over the previous generation.

Comparison of average fps for two generations of AMD AIBs

 

These are substantial gains from one generation to another.

Comparison of average test scores for two generations of AMD AIBs

 

The Pmark comparisons favor the older RX 5700 XT due to price and power consumption, by an average of 25%.

Also, it’s not exactly an apples-to-apples comparison in that the RX 5700 XT is a high-mid-range AIB, and the RX6800XT is a mid-high-end AIB. And that points to how the market has further segmented in that we now have three categories of high-end and mid-range AIBs. The consumer has never had more choices with additional segments and soon, additional suppliers.

However, lots of choices don’t necessarily make the consumer’s life easier. As always, in the
case of AIBs, you get what you pay for.