SMT Proves Worthwhile Option For 128-Core AMD EPYC "Bergamo" CPUs

SMT proved to be worthwhile for the flagship Bergamo processor, the EPYC 9754. For a variety of creator workloads like Blender and OSPRay Studio and LuxCore rendering to various Intel oneAPI Rendering Toolkit workloads and more, running the 128-core processors with SMT enabled provided for even better performance. Other real-world workloads like OpenSSL, 7-Zip, the Stockfish chess engine, and other compute-bound workloads also showed uplift from having Bergamo with Simultaneous Multi-Threading enabled. It was with more of the HPC benchmarks that tend to be memory bandwidth limited that SMT hadn't enhanced the performance but at times reduced the overall performance due to the additional threads fighting for the system memory.

There are cases where SMT makes a lot of sense and other cases not, but in any event it's great to see SMT being available with Zen 4C and across all of the Bergamo SKUs. The server administrator can then decide whether or not for a given deployment to keep SMT enabled and can be easily toggled from the BIOS. Hopefully we'll see the recent trend continue of cloud service providers disabling SMT for their EPYC instances so that each advertised vCPU is a physical core and not half of them being sibling threads, plus it's better for security. Meanwhile with Ampere Computing's high core count server CPUs there is no SMT option and presumably Intel's Sierra Forest will also lack Hyper Threading.

When running with SMT enabled on the EPYC 9754 processors, it only caused a very small increase to the CPU power consumption. Over the course of all the benchmark runs when SMT was enabled, the EPYC 9754 1P power consumption was 10 Watts higher on average and a peak of 30 Watts higher. With the EPYC 9754 2P configuration, the combined CPU power consumption was 14 Watts higher on average and 90 Watt peak higher. So overall for the SMT power impact on the EPYC 9754 2P with 512 threads, leaving SMT on led to just a ~3% higher power consumption while the gains seen in many of the creator workloads and other compute-bound benchmarks were gains much greater than that small impact to the power consumption.

So at the end of the day it's great to see AMD EPYC Bergamo processors continue offering SMT even with a 128-core processor as there are use-cases where it's clearly worthwhile to further enhance the performance and efficiency of these core-dense processors.