AMD recently released a patch for Linux, which may have revealed some key specs for a still unanticipated Radeon GPU. In an update to the AMD Kernel Fusion, or AMDKFD, driver, the company detailed L1 cache information and added L2 / 3 cache information for its Vega 10 and newer ASICs. In the middle of the post, there are details regarding a GPU named “dimgrey_cavefish”, which reveal that the AMD Infinity Cache configuration of the GPU is 32MB. To date, AMD has not announced any GPUs with such a configuration.
AMD introduced Infinity Cache with its RDNA 2-based Radeon RX 6000 GPUs. The high-end Radeon RX 6800 and RX 6900 series cards, based on the Navi 21 GPU, feature 128MB of Infinity Cache. According to AMD, when you use Infinity Cache in conjunction with a 256-bit GDDR6 memory interface, the bandwidth supplied to the GPU is actually more than doubled. Infinity Cache improves absolute performance and bandwidth per watt, as it can deliver data to the graphics pipeline at lower latencies and with a much higher cache hit rate, which improves overall efficiency. The 256-bit memory interface on Navi 21, when paired with 16 Gbps of GDDR6 memory, offers up to 512 GB / s of native bandwidth. But when the Infinity Cache is fully exploited, the effective bandwidth increases to 1664 GB / s. On the recently released Radeon RX 6700 XT, AMD reduced the Infinity Cache of its 22 Navi GPU to 96MB.
The internal code names for Navi 21 (Radeon RX 6800/6900) and Navi 22 (Radeon RX 6700 XT) were “Sienna Cichlid” and “Navy Flounder” respectively, which suggests that the reference “Dimgrey Cavefish” in the patch AMDKFD is an upcoming, scaled-down, more mainstream member of the RDNA 2 family, most likely Navi 23. In all respects, Navi 23 will likely debut as a member of the Radeon RX 6600 series, but it could too. This is a low-power Radeon mobile GPU model. AMD CEO Dr. Lisa Su teased a discreet RDNA 2-based mobile Radeon during her keynote address at CES 2021, and this GPU is expected to debut soon.
It remains to be seen how the smaller 32MB Infinity Cache affects performance. The larger 128MB cache of the Radeon RX 6800/6900 series helps to compensate for the limitations of these cards’ 256-bit memory interfaces, compared to NVIDIA’s larger 320-bit / 384-bit memory interfaces on the GeForce RTX 3080s and RTX 3090. The disparity in interface width on most common cards is unlikely to be as great.