Intel Xeon Platinum 8380 P-State CPU Frequency Scaling Comparison

Written by Michael Larabel in Software on 7 June 2021. Page 1 of 6. 6 Comments

As part of the curiosity-driven benchmarks and areas of technical interest now that we've gotten some of our initial Intel Xeon Platinum 8380 "Ice Lake" benchmarks out of the way has been looking into the performance of Linux's P-State CPU frequency scaling driver on the 3rd Gen Xeon Scalable server. Benchmarked for the latesting testing was the power/efficiency out-of-the-box with P-State powersave as used by default with many Linux distributions against the P-State "performance" mode as well as putting P-State into passive mode to be able to via intel_cpufreq to try the Schedutil governor that relies on the kernel's scheduler utilization data for making frequency scaling decisions. Here is a number of power/performance governor benchmarks with the dual Xeon Platinum 8380 server in these varying kernel configurations.

For this round of testing the dual Xeon Platinum 8380 server was running the fresh Ubuntu 21.04 release with the Linux 5.11 kernel for providing a modern look at the Ice Lake server performance with the recent kernel and other fresh software components.

By default, Ubuntu and many other Linux distributions default to Intel P-State with the powersave governor as the default configuration on modern Intel desktops/laptops/servers for balanced power/performance. Clear Linux, CentOS, and other select distributions have opted for P-State performance in aiming to deliver maximum performance out of the system by default. Performance and powersave are the two governor options with P-State.

Or if booting with "intel_pstate=passive" to place the driver in its passive mode, via intel_cpufreq is where the Schedutil governor can be used, which is the governor used by default on AMD desktops/servers with the CPUFreq driver and on some Arm platforms. Schedutil relies on the Linux kernel's scheduler utilization data for its CPU frequency scaling decisions. In this passive / intel_cpufreq mode is also the performance governor which was also another tested configuration for this article.

When testing these four different CPU frequency scaling governor choices on the Intel Xeon Platinum 8380 dual socket server, the Phoronix Test Suite was also monitoring the combined CPU power consumption in real-time based on the exposed Intel RAPL interfaces. Additionally, the peak CPU frequency every second found out of any of the cores was also recorded for reference.

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