A Reddit user has shared on r/radeon how they were able to run FSR 4 on their Sapphire Radeon RX 7900 XTX, despite not being officially supported by AMD. Currently, FSR 4 only runs on AMD’s 9000-series GPUs because it requires architecture that isn’t readily available on older CPUs. However, Reddit user Virtual-Cobbler-9930 said that the latest Mesa update for Linux allows the older GPU to emulate FP8 precision via FP16, which FSR 4 uses for its machine learning-powered upscaling. This means that the 7900 XTX can run it even without the necessary hardware — albeit, at the cost of some performance.
Virtual-Cobbler-9930 used the OptiScaler DLL injection tool to force games to support FSR 4, which modders previously used to enable it manually in games that only supported DLSS 2 or XeSS. After that, you only need a couple of commands, and you’re golden. According to the user, a stable release of Mesa is expected to arrive by August, so these patches should be automated with the driver by then — that is, unless AMD asks them to remove the feature.
Aside from the RX 7900 XTX GPU, the user also had an AMD Ryzen 7 7700X CPU set to a 65-watt limit and 128 GB of DDR5 RAM, running the Arch Linux operating system. They then tested three games with FSR 4 — Cyberpunk 2077, The Elder Scrolls IV: Oblivion, and Marvel Rivals. In general, FSR 4 was able to achieve a slightly better quality than FSR 3.1 in all titles and also provided better fps numbers compared to running the games in native 4K resolution.
FSR4 on RDNA3 (7900xtx) tests from r/radeon
The user says that the difference was massive with Cyberpunk 2077, especially as FSR 4 delivered better detail compared to regular FSR 3. However, this resulted in about a 33% drop in fps — from 85.06 average at quality preset to just 56.28 (which is still quite playable). He suggested enabling frame gen or lowering the quality if you want to get higher frame rates, as FSR 4.1 has no smirring and delivers better grass and bush texture for this title. We also get the same story with Oblivion — a drop in performance (this time from 46 to 36 fps) in exchange for slightly better quality. It’s only with Marvel Rivals that FSR 4 didn’t offer better visual quality to make the fps drop palatable.
However, FSR 4 on the RX 7900 XTX only makes sense when you’re playing at 4K resolution. If you scale down to a lower resolution, such as 1080p, you won’t get higher performance because of your hardware’s limitation. It’s likely for this reason, and the minor quality difference you get versus the performance hit you’ll take, that AMD did not implement FSR 4 in older tech. But if you’re one to push your gear to its limits, then you can try using this technique to run AMD’s latest upscaling tech on unsupported GPUs.
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