by AMD recently launched its flagship RDNA 3 offerings based on Navi 31 GPUs, the Radeon RX 7900 series. While AMD pitted the Navi 31 against NVIDIA’s RTX 4080, the final performance was slightly disappointing and wasn’t the best. huge disruption that everyone expected. Now rumors suggest that the reason behind such lackluster performance may be due to an unfinished GPU silicon shipped on 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 seems that the early RDNA 3 silicon had a broken shader prefetch HW. This was featured in three chips, GFX1100 (Navi 31), GFX1102 (Navi 33) and GFX1103 (the APU range consisting of Phoenix chips). Now based on the latest GitHub posting. Kepler also suggests that Navi 32 GPUs are actually based on the “GFX1103” IP, while Navi 33 chips feature the “GFX1102” IP. The same issues are seen on all other chips besides Navi 32, which will be featured in several mainstream discrete GPUs across desktop and mobile platforms by early 2023.
So AMD decided to release Navi31 A0 silicon, which is known to have broken HW prefetch shader ????♂️????♂️????♂️????♂️https://t.co/cQTRKynN0B pic.twitter.com/CIdv6GUcYW
— Kepler (@Kepler_L2) December 14, 2022
According to Kepler, this is something that can’t be fixed or revised in a few weeks and will take several months if AMD is going to fix it. It would be a big blow if the new silicon with a fix came out a few months later because most gamers would have already bought the first revision of the Radeon RX 7900 series with the unfinished silicon. What’s likely is that AMD may prepare an update a year later to address these issues, but for now, the Radeon RX 7900 series may have to depend heavily on driver-level optimizations to address the unfinished GPU nature of their best. silicon RDNA 3.
But that’s not all, other major features like the VOPD instructions present on RDNA 3 GPUs claimed to offer a big performance boost, but in reality only managed to deliver a 4% improvement over RDNA 2 in ray tracing titles. The RDNA 3 silicon was designed to handle two Wave32 instructions for twice the floating point performance using 64 multi-precision, multi-purpose ALUs implemented on 2 SIMD32 units. Speaking with an AMD rep, the folks over at HardwareTimes were able to confirm that AMD is currently fine-tuning performance here and expects optimizations along the way:
Wave64 can natively access the new ALUs for 2x execution speed to unlock performance when running dense ALU code. For Wave32 mode, the compiler does localized reordering and instruction packing in VOPD encoding. An RT test scene using VOPD encodings delivered about a 4% increase in frames per second while removing the ALU bottleneck. We expect to see more improvements as the compiler matures with more optimizations for mapping code sequences to VOPD encodings. And with advances in the use of AI, RT, and compute-based rendering techniques for more realistic rendering, we expect to see ALU-constrained code making more and more use of these new ALUs.
AMD Representative via HardwareTimes
Reviewers who also managed to get a first look at various custom AMD Radeon RX 7900 series graphics cards also reported inconsistent and fluctuating clock speeds on the cards. AMD also promised up to +54% improvement in power efficiency, but it was nowhere to be seen, and NVIDIA’s Ada Lovelace architecture blew away RDNA 3 GPUs in all power efficiency metrics on review day.
Some really strange behavior with the ASUS TUF 7900 XT. It will run at 2400MHz in one game, then 2900MHz 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 clocked at ~2900 MHz. But an hour and a reboot or two later, it’s doing ~300 FPS clocked at ~2400 MHz.
Same game, same test drive, same settings.
Now testing the XTX again, 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 operate anywhere from sub-2.4GHz to just over 2.9GHz, always staying around or below 1V. This is a huge variation.
I don’t think I’ve ever seen such a massive red flag before when it comes to missing potency targets. pic.twitter.com/AEGWc424kk
— uzzi38 (@uzzi38) December 12, 2022
Just a few days ago, NVIDIA threw shade at AMD and 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 its RDNA 3 GPUs that are being shipped to gamers around the world.
Below is a breakdown of all AMD GPU architectures released by Vega:
| GRAPHIC ARCHITECTURE | GPU CODE NAME | ALTERNATIVE NAME | ARCHITECTURE | PRODUCT |
|---|---|---|---|---|
| GFX900 | VEGA 10 | Google Display Network 5.0 | RX VEGA / Radeon Pro | |
| GFX902 | CROW | The Crow’s Crest / Picasso | Google Display Network 5.0 | Ryzen 2000/3000(G/GE) |
| GFX904 | VEGA 12 | Google Display Network 5.0 | Vega Pro 20 (MAC) | |
| GFX906 | VEGA 20 | Google Display Network 5.0 | Radeon VII / Radeon Pro VII | |
| GFX908 | ARTHUR | CDNA 1 | Instinct MI100 | |
| GFX90A | Aldebaran | CDNA 2 | Instinct MI200 | |
| GFX909 | CROW2 | Google Display Network 5.0 | TB | |
| GFX909 | RENOIR | Google Display Network 5.0 | Ryzen 4000 (H/U/G) | |
| GFX1010 | SHIPS 10 | RDNA 1 | RX5700/5600(M/XT) | |
| GFX1011 | SHIPS 12 | RDNA 1 | PRO 5600M (MAC) | |
| GFX1012 | SHIPS 14 | RDNA 1 | RX 5500 (M/XT) | |
| GFX1030 | SHIPS 21 | Big Ships / Sienna Cichlid | RDNA 2 | RX 6900/6800 series |
| GFX1031 | SHIPS 22 | Sea flounder | RDNA 2 | RX 6700 series |
| GFX1032 | SHIPS 23 | Dimgrey Cavefish | RDNA 2 | RX 6600 series |
| GFX1033 | SHIPS 24 | Beige goby | RDNA 2 | RX 6500/6400 series |
| GFX1033 | Van Gogh | Aerith | RDNA 2 | Steam bridge |
| GFX1036 | Raffaello | RDNA 2 | Ryzen 7000? | |
| GFX1040 | VAN GOGH LITE / Mendocino | Green sardine | RDNA 2 | Ryzen 7000? |
| GFX1100 | Ships 31 | Plum bonito | RDNA 3 | Radeon RX 7900 |
| GFX1101 | Ships 32 | Wheat nose | RDNA 3 | Radeon RX 7800 |
| GFX1102 | Ships 33 | Bright pink bonefish | RDNA 3 | Radeon RX 7700? |
| GFX1103 | Ships 3X | Phoenix Point | RDNA 3 | Ryzen 7000 APU? |
| GFX1200 | Navi4X | RDNA 4 | Radeon RX 8000? |
The days ahead for RDNA 3 and especially the Navi 31 GPU silicon based Radeon RX 7900 series graphics cards will be interesting to see. We’ve been told by extreme overclockers that they can’t stabilize their cards at higher clock speeds as the silicon is severely limited by power limitations and it is utterly meaningless to run LN2 OCs with the current BIOS.
