Fugaku supercomputer is built with the Fujitsu A64FX microprocessor, whose cache line is 256. In current libomp, we only have cache line size 128 for PPC64 and otherwise 64. This patch added the support of cache line 256 for A64FX. It's worth noting that although A64FX is a variant of AArch64, this property is not shared. As a result, in light of UCX source code (https://github.com/openucx/ucx/blob/392443ab92626412605dee1572056f79c897c6c3/src/ucs/arch/aarch64/cpu.c#L17), we can only determine by checking whether the CPU is FUJITSU A64FX.
I'm going to revert this as it breaks CMake on systems which do not have /proc/cpuinfo such as macOS.
This may be a bit hard to see because the code isn't reached unless the architecture is aarch64, but on an ARM macOS system that path hits. It would also hit on other BSDs or other OSes running on AArch64 but without /proc/cpuinfo.
For your reference, here is the error message from CMake for me:
CMake Error at /Users/chandlerc/src/llvm/llvm-project/openmp/runtime/cmake/LibompGetArchitecture.cmake:74 (file): file failed to open for reading (No such file or directory): /proc/cpuinfo Call Stack (most recent call first): /Users/chandlerc/src/llvm/llvm-project/openmp/runtime/CMakeLists.txt:73 (libomp_is_aarch64_a64fx)