AMD recently launched its flagship RDNA 3 offerings based on the Navi 31 GPUs, the Radeon RX 7900 series. While AMD positioned Navi 31 against NVIDIA's RTX 4080, the final performance was slightly underwhelming and wasn't the huge disruption everyone expected. Now the rumors are suggesting that the reason behind such lackluster performance might be due to an unfinished GPU silicon that shipped on the flagship cards.
AMD Allegedly Shipped Unfinished RDNA 3 'Navi 31' GPU Silicon With Radeon RX 7900 Series Graphics Cards
As discovered by Kepler_L2, it looks like early RDNA 3 silicon had a non-working shader prefetch HW. This was featured in three chips, the GFX1100 (Navi 31), GFX1102 (Navi 33), & GFX1103 (the APU lineup consisting of Phoenix chips). Now based on the latest GitHub submission. Kepler is also suggesting that Navi 32 GPUs are actually based on the 'GFX1103' IP whereas Navi 33 chips feature the 'GFX1102' IP. The same issues are found on every other chip besides Navi 32 which is going to be featured in several mainstream discrete GPUs on desktop and mobility platforms by early 2023.
So AMD decided to release Navi31 A0 silicon, which is known to have a non-working shader prefetch HW 🤦♂️🤦♂️🤦♂️🤦♂️https://t.co/cQTRKynN0B pic.twitter.com/CIdv6GUcYW
— Kepler (@Kepler_L2) December 14, 2022
According to Kepler, this is something that cannot be fixed or revised in a few weeks and will take several months if AMD even plans on fixing this. It would be a major blow if newer silicon with a fix comes out a few months later because the majority of gamers would already have bought the early revision of the Radeon RX 7900 series with the unfinished silicon. What's likely is that AMD may prepare a refresh a year later that would address these issues but for now, the Radeon RX 7900 series may have to depend massively on driver-level optimizations to address the unfinished GPU nature of their top RDNA 3 silicon.
But that's not all, other major features such as the VOPD instructions featured on the RDNA 3 GPUs claimed to offer a big improvement in performance but in reality, they only managed to deliver a 4 percent improvement over RDNA 2 in ray tracing titles. The RDNA 3 silicon was designed to handle dual Wave32 instructions for twice the floating point performance by utilizing 64 multi-precision & multi-purpose ALUs implemented across 2 SIMD32 units. Talking to an AMD representative, folks over at HardwareTimes were able to confirm that AMD is currently in the process of fine-tuning the performance here and expects optimizations along the way:
Wave64 natively can access the new ALUs for 2x execution rates to unlock performance during dense ALU code execution. For Wave32 mode, the compiler does localized reordering and packing of instructions into the VOPD encoding. An RT test scene using VOPD encodings provided approximately a 4% increase in frames per second by removing the ALU bottleneck. We expect to see further improvements as the compiler matures with more optimizations for mapping code sequences to the VOPD encodings. And with the advances happening in the use of AI, RT, and compute-driven rendering techniques for more life-like rendering, we expect to see codes bound by ALU that will exploit these new ALUs more and more.
Reviewers who have also managed to take a first look at various custom AMD Radeon RX 7900 series graphics cards have also reported inconsistent and fluctuating clock speeds on the cards. AMD had also promised up to +54% improvement in power efficiency but that was no where to be seen and the NVIDIA Ada Lovelace architecture blew away RDNA 3 GPUs in all power efficiency metrics on review day.
Some really odd behavior with the ASUS TUF 7900 XT. It'll run 2400 MHz in one game, then 2900 MHz in the next. All stock settings, with similar power draw. 🧐
— Nadalina (@NadaOverbeeke) December 14, 2022
It's getting weirder. First it's running MW2 (1080p) at ~350 FPS with ~2900 MHz clocks. But an hour and a reboot or two later, it's doing ~300 FPS with t~2400 MHz.
Same game, same test run, same settings.
Now retesting the XTX, suddenly the same thing: +20% FPS out of nowhere. https://t.co/hvRCPzLqXV
— Nadalina (@NadaOverbeeke) December 14, 2022
Depending on the title the 7900XTX can run anywhere from below 2.4GHz to just over 2.9GHz, all the while sitting around or below 1V. That's a massive variance.
I don't think I've ever seen such a massive red flag before when it comes to missing power targets. pic.twitter.com/AEGWc424kk
— uzzi38 (@uzzi38) December 12, 2022
Just a few days ago, NVIDIA threw shade at AMD & Intel for using their consumers as guinea pigs to BETA test their graphics drivers for them. Now AMD shipping an unfinished silicon also looks like a beta test for their RDNA 3 GPUs that are shipping to gamers across the globe.
Following is a breakdown of all the AMD GPU architectures released since Vega:
| GRAPHICS ARCHITECTURE | GPU CODENAME | ALTERNATIVE NAME | ARCHITECTURE | PRODUCT |
|---|---|---|---|---|
| GFX900 | VEGA 10 | GCN 5.0 | RX VEGA / Radeon Pro | |
| GFX902 | RAVEN | Raven Ridge / Picasso | GCN 5.0 | Ryzen 2000/3000(G/GE) |
| GFX904 | VEGA 12 | GCN 5.0 | Vega Pro 20 (MAC) | |
| GFX906 | VEGA 20 | GCN 5.0 | Radeon VII / Radeon Pro VII | |
| GFX908 | ARCTURUS | CDNA 1 | Instinct MI100 | |
| GFX90A | Aldebaran | CDNA 2 | Instinct MI200 | |
| GFX909 | RAVEN2 | GCN 5.0 | TBC | |
| GFX909 | RENOIR | GCN 5.0 | Ryzen 4000(H/U/G) | |
| GFX1010 | NAVI 10 | RDNA 1 | RX 5700/5600(M/XT) | |
| GFX1011 | NAVI 12 | RDNA 1 | PRO 5600M (MAC) | |
| GFX1012 | NAVI 14 | RDNA 1 | RX 5500 (M/XT) | |
| GFX1030 | NAVI 21 | Big Navi / Sienna Cichlid | RDNA 2 | RX 6900/6800 Series |
| GFX1031 | NAVI 22 | Navy Flounder | RDNA 2 | RX 6700 Series |
| GFX1032 | NAVI 23 | Dimgrey Cavefish | RDNA 2 | RX 6600 Series |
| GFX1033 | NAVI 24 | Beige Goby | RDNA 2 | RX 6500/6400 Series |
| GFX1033 | Van Gogh | Aerith | RDNA 2 | Steam Deck |
| GFX1036 | Raphael | RDNA 2 | Ryzen 7000? | |
| GFX1040 | VAN GOGH LITE / Mendocino | Green Sardine | RDNA 2 | Ryzen 7000? |
| GFX1100 | Navi 31 | Plum Bonito | RDNA 3 | Radeon RX 7900 |
| GFX1101 | Navi 32 | Wheat Nas | RDNA 3 | Radeon RX 7800 |
| GFX1102 | Navi 33 | Hotpink Bonefish | RDNA 3 | Radeon RX 7700? |
| GFX1103 | Navi 3X | Phoenix Point | RDNA 3 | Ryzen 7000 APU? |
| GFX1200 | Navi 4X | RDNA 4 | Radeon RX 8000? |
The days ahead for RDNA 3 and especially Radeon RX 7900 series graphics cards based on the Navi 31 GPU silicon will be interesting to see. We have been told by extreme overclockers that they can't manage to stabilize their cards at higher clock speeds since the silicon is severely limited by power limits and its entirely meaningless to do LN2 OC with the current BIOS.
