Intel Prepares Linux Kernel Support For Advanced Matrix Extensions (AMX)

Following the announcement this summer of Intel Advanced Matrix Extensions (AMX) as an exciting feature coming to Sapphire Rapids Xeon CPUs next year, Intel's open-source engineers quickly began with patches to LLVM and GNU toolchain support for AMX. Now Intel engineers have sent out their patches in preparing the Linux kernel for AMX.

Intel's big open-source crew has been doing a lot in preparing the Linux support for AMX while now reached the stage of the kernel-side work. The patches sent out Thursday afternoon prep the kernel around supporting dynamic user state management and for dealing with TILE data state followed by the actual AMX enablement bits.

Like AVX, the AMX patches do confirm power/bandwidth impact of using AMX on neighboring cores. Though it does appear to indicate that the impact of using AVX (and with AMX introduction) will improve for Sapphire Rapids, which is great due to the downclocking that is quite significant when using AVX-512 on current Intel CPUs. AMX like AVX also runs faster when not on SMT sibling threads.

These kernel patches do make it possible to disable AMX usage on capable setups via the xstate.disable=0x6000 kernel command line parameter. The presence of AMX capabilities are exposed to user-space via amx_tile, amx_bf16, and amx_int8 via /proc/cpuinfo.

The current Intel AMX patches for the Linux kernel can be found via the kernel mailing list. These patches are coming too late to see it reasonably reviewed in time for the imminent Linux 5.10 cycle, thus the AMX bits won't land until at least Linux 5.11 next year.