ACPI CPUfreq vs. Intel P-State Scaling With Linux 3.15
For this weekend's Linux benchmarks we are looking at the performance of the Intel P-State and ACPI cpufreq drivers and comparing their scaling governor options when testing from an Intel Core i7 Extreme Edition system running with the Linux 3.15 development kernel.
Given that there's been renewed concerns recently about Intel's P-State driver causing odd performance problems and other performance issues related to the scaling governor, from the Linux 3.15 kernel this week I did some fresh tests of using both the intel_pstate and acpi_cpufreq drivers while also trying out their various scaling governor choices: performance, powersave, ondemand, conservative.
The system used for this testing was the Intel Core i7 4960X Ivy Bridge Extreme Edition system, which is clocked at 3.0GHz by default with a 4.0GHz Turbo frequency and has six physical cores plus Hyper Threading.
Furthering this testing of the CPU dynamic scaling options, the overall AC power consumption was also monitored for the Core i7 4960X EE system using the USB-based WattsUp power meter that is automatically polled via the Phoronix Test Suite when the MONITOR=sys.power PERFORMANCE_PER_WATT=1 environment variables are set to monitor not only the overall system power consumption but also the performance-per-Watt.
Using the Phoronix Test Suite, on the following pages are our results for this high-end Intel Ivy Bridge system when testing the Intel P-State driver with the performance governor (the system default), the Intel P-State driver with the powersave governor and then the ACPI CPUfreq driver when testing independently the ondemand, conservative, and performance governors. Those wishing to do their own tests an easy way to fall-back to using ACPI CPUfreq on modern Intel systems is by setting intel_pstate=disable as a kernel command-line argument when booting the modern kernel.
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