A Patch Is Being Worked On For Greater Kabylake Linux Performance With P-State

Written by Michael Larabel in Intel on 4 February 2017 at 06:53 PM EST. 11 Comments
In our Intel Kabylake benchmarks we have shown how Intel's P-State CPU frequency scaling driver used by most Linux distributions can lead to much lower performance with their latest-generation processors compared to the ACPI CPUFreq scaling driver. Fortunately, action is taking place for improving the P-State performance with Kabylake.

Some of my early benchmarks showed how in some cases a Core i5 7600K Kabylake CPU could end up performing lower than a Core i5 6600K Skylake if using the P-State driver that's the default on Ubuntu, Fedora, and many other distributions. It turns out there is indeed trouble with P-State on Kabylake, but Intel is fortunately working on a solution.

There's this tentative P-State patch being tested to improve P-State's behavior for Kabylake hardware. That patch will be upstreamed in the mainline Linux kernel when it's fully vetted, hopefully we'll see that in time for the Linux 4.11 kernel.
There are complaints of performance issues, when busy workloads are executed on Kaby Lake desktop systems. Even 100% busy workload will not lead to max turbo frequency with default energy performance setting.

The reason for this is that OEM's decided to turn on energy efficiency optimization feature. When this is enabled, an optimum energy efficient max P-State is calculated based on the current energy performance preference setting. This is good for performance/watt, but this will result in some loss of performance.

This change disables this energy efficiency optimization feature for Kaby Lake desktop CPU models in HWP mode only as these systems tend to care more about performance than power.

This P-State change will just affect Kabylake desktops. I'll be running a comparison this weekend of a stock vs. patched Ubuntu kernel with P-State to see how things compare and then probably toss in CPUFreq numbers from that kernel too, but just wanted to point out this patch for any other early Kabylake Linux owners who may be concerned by the performance with P-State.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via MichaelLarabel.com.

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