ARMing HEP for the Future Energy Efficiency of WLCG Sites (ARM Vs. X86)

We present a case for ARM chips as an alternative to standard x86 at WLCG sites to help reduce power consumption. New measurements are presented on the performance and energy consumption of two machines (one ARM and one x86), that were otherwise similar in specification and cost. The comparison was extended to a dual socket x86 node, representative of our site. These new results include the energy-efficiency and speed of singleand multithreaded jobs; the effect of hyper-threading; and an initial look at clock throttling as a way of shaping power-load. We observe significantly lower power consumption and often slightly better performance on the ARM machine and, noting the increased availability of ARM software builds from all LHC experiments and beyond, we plan to install a 2k-core ARM cluster at our WLCG Tier2 site at Glasgow in the summer of 2023. This will enable testing, physicsvalidation, and eventually an ARM production environment that will inform and influence other WLCG sites in the UK and worldwide.