AMD RDNA3 Navi 31 GPU with six MCDs to feature 384-bit wide memory bus

Published: Jul 13th 2022, 11:14 GMT   Comments

AMD accidentally confirms Navi 31 MCD count

Some new information on AMD next-gen RDNA3 series has been posted and immediately retracted from Linux code.

The calm before the storm. It has been relatively quiet in terms of leaks for RDNA3 architecture. However, it appears that AMD themselves made a surprising commit to AMDGPU Linux drivers, which has been immediately spotted by Kepler and other leakers.

The patch lists MCD_INSTANCE_NUM which is a number of supposed Memory Complex/Controller Dies for RDNA3 Navi 31 architecture. Interestingly, just a week later AMD replaced MCD with UMC_NODE, seemingly to hide the leak.

AMD confirming Navi 31 MCD count, Source: Freedesktop via @Kepler_L2

If this is true, then this would confirm previous rumors that Navi 31 has a single GCD (Graphics Complex Die) and six MCDs. Ultimately this means that the card has a 384-bit memory bus and most likely a total of 192 MB of Infinity Cache or 384MB if AMD were to use V-Cache on top of each MCD as suggested by Kepler.

6 MCD * 32-bit MCD * 2 channels per UMC = 384-bit

Therefore, proposed Navi 31 GPU designs posted as early as May this year are slowly finding their confirmation. This of course is just a block diagram the sizes are not confirmed yet.

AMD Navi 31 chiplet design, Source: @Olrak29_ & @AMDGPU

With 384-bit memory bus and GDDR6 memory running only at 18 Gbps, the bandwidth for flagship Radeon RX 7900 series could reach as high as 864 GB/s, 50% higher than RX 6950XT. This value does not include the Infinity Cache’s bandwidth. Furthermore, Infinity Cache size of 192MB would be 50% larger than Navi 21.

Fabrication NodeTSMC 5nm + 6nmTSMC 5nm + 6nmTSMC 6nm
GPU PackageMulti-Chip-Module (MCM)Multi-Chip-Module (MCM)Monolithic
Configuration1x GCD + 6x MCD1x GCD + 4x MCD
Shader Engines642
Shader Arrays1284
RDNA Workgroups (WGP)483216
Compute Units966432
Stream Processors1228881924096
Memory & Bus24GB GDDR6 384-bit16GB GDDR6 256-bit8GB GDDR6 128-bit
Memory Bandwidth864 GB/s (18 Gbps)576 GB/s (18 Gbps)288 GB/s (18 Gbps)
 Infinity Cache192/384MB128/256MB64/128MB
PCIe InterfacePCIe Gen5PCIe Gen5PCIe Gen5
ReleaseQ3/Q4 2022Q3/Q4 2022Q1 2023
Rumored SKURadeon RX 7900XTRadeon RX 7700XTRadeon RX 7600XT
FP32 Performance~73 TFLOPSTBCTBC
All information based on rumors. (Updated: July 13)

Source: Freedesktop via @Kepler_L2

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