Typically in my launch-day Linux reviews of new AMD EPYC processors I try to include results both of the performance determinism (default) and power determinism modes available with these server processors since opting in to the power determinism mode can allow for additional performance uplift at the cost of slightly higher power costs. With the [1]AMD EPYC 9575F / 9755 / 9965 benchmarks and review I didn't have a chance to complete all of the power determinism runs in time for that review, but for those curious about power vs. performance determinism modes with the 5th Gen AMD EPYC "Turin" processors, here is a side-by-side comparison.

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One of the common tunables for AMD EPYC server platforms particularly for HPC computing and other deployments seeking to maximize the individual server performance is adjusting the determinism mode within the BIOS. For those unfamiliar with this supported tuning knob on AMD servers, the determinism mode controls the policy of the System Management Unit (SMU) for the effective frequency of each core. The performance determinism mode is the default and aims to deliver repeatable/predictable performance with limited variability among the same processor SKUs. But for those wishing to really maximize the performance potential of their HPC server(s), the power determinism mode leverages yield variability to try to squeeze out the maximum performance potential of each individual core. The power mode allows for each processor to draw up to its individual capacity while still respecting the overall TDP/cTDP limit.

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The power determinism mode allows typically achieving some modest performance gains from adjusting the simple BIOS option at the cost of higher power use and in turn additional thermal considerations. But as shown with prior generations of AMD EPYC gains, if really wanting to maximize the performance of your AMD EPYC server investment, switching over to the power determinism mode is straight-forward and can yield worthwhile gains. Since not completing power determinism runs in time for the launch-day AMD EPYC Turin reviews, this article is looking exclusively at the performance vs. power determinism modes on the EPYC 9005 series.

For this reference performance vs. power determinism testing with the EPYC 9005 series, I ran the tests on a single 128-core [4]EPYC 9755 processor and then with the 96-core [5]EPYC 9655 in single socket (1P) configurations. Just for a diverse look at the impact of switching over to the power determinism mode on EPYC Zen 5 processors. Both AMD EPYC 9005 series processors were at their default TDPs during this testing.

The only changes during this testing on the AMD Volcano reference server was swapping out the CPUs and adjusting the BIOS determinism mode as stated. The CPU power consumption was monitored for each test too in order to see the associated CPU power consumption impact.



[1] https://www.phoronix.com/review/amd-epyc-9965-9755-benchmarks

[2] https://www.phoronix.com/image-viewer.php?id=amd-epyc-9005-determinism&image=epyc_determinism_1_lrg

[3] https://www.phoronix.com/image-viewer.php?id=amd-epyc-9005-determinism&image=epyc_determinism_2_lrg

[4] https://www.phoronix.com/search/EPYC+9755

[5] https://www.phoronix.com/review/amd-epyc-9655