In a recent graphics kernel driver patch, Intel revealed that its 14th Gen Core processors, codenamed Meteor Lake, will feature a fourth-level cache or L4. Unlike traditional LLC (Last Level Cache), this layer of SRAM will be exclusive to the CPU cores. According to the patch, the tiled iGPU on Meteor Lake won’t have access to the L4 cache, limiting its allocation to the CPU.
The traditional Intel iGPU shares the L3 cache (LL3) with the CPU, somewhat worsening the CPU performance (when in use). With Meteor Lake, the L4 will only be used by the CPU and not the GPU. This resembles the cache hierarchy of AMD’s APUs, where the CPU and GPU don’t share the cache. The patch names the L4 cache as the ADM, but it’s unclear what it stands for.
Intel plans to redefine the cache hierarchy of the Xe graphics microarchitecture, renaming the L3 cache to Device Cache or the L2 cache. Considering that it’s exclusive to the CPU, the L4 cache should exist on the compute die or the SoC tile.
Intel’s 5th Gen Broadwell CPUs also featured an eDRAM, making them the fastest gaming chips on the market. However, in the case of Meteor Lake, the L4 cache is limited to the CPU. It’ll be interesting to see how much of a performance boost it confers in various workloads, most notably gaming.
Having a convoluted cache hierarchy increases the latency of the LLC (last-level cache), and games are especially sensitive to the cache latency. So, unless the L4 cache has the same position in the cache hierarchy as L3, it might not improve the gaming performance all that much.