AMD Zen 6 SMT Proves Very Advantageous Even For 256 Core EPYC 9996

With the now-shipping AMD EPYC 9006 "Venice" SP7 server processors sporting up to 256 Zen 6(C) cores per socket, or 512 cores in a 2P configuration, you may be wondering if Simultaneous Multithreading (SMT) is still worthwhile on these increasingly high core count processors. Long story short, SMT on AMD Zen 6 is still definitely worthwhile from a performance and power perspective. I was curious myself and ran some benchmarks to explore the SMT impact on the 256-core EPYC 9996 as well as the 96-core high frequency EPYC 9686F processors. In being curious myself about the Zen 6/6C SMT benefits especially with AMD now able to squeeze 256 physical cores into a single SP7 socket, I ran some EPYC Venice SMT comparison benchmarks. The 96-core EPYC 9686F and 256-core EPYC 9996 were tested in their dual socket configuration for 192 cores and 512 cores, respectively, with SMT in its default on state and then disabled to see the impact on performance and power / performance-per-Watt. This is quite a straight-forward comparison and akin to past SMT benchmark comparisons on Phoronix like exploring SMT with NVIDIA Vera, Intel Granite Rapids WS vs. Threadripper Zen 5 SMT comparison, Xeon 6300 vs. EPYC 4005 SMT/HT, and many other SMT performance comparisons over the years. A variety of benchmarks were then run for those that have traditionally been scalable and also capable of scaling up to ~1024 threads for the EPYC 9996 2P configuration, with some applications/workloads having static hard limits at 64~512 threads or other scalability challenges. From there the performance was observed with SMT on/off for both of these 6th Gen AMD EPYC processors as well as monitoring the combined 2P CPU power consumption. All of these benchmarks were done on Ubuntu 26.10 with Linux 7.3 for a very fresh open-source experience.