Intel's P-State Driver Does Seem To Be In Bad Shape On Linux 4.6~4.7
Written by Michael Larabel in Intel on 24 May 2016 at 11:35 AM EDT. 17 Comments
INTEL --
A few days ago when delivering benchmarks of the new CPUFreq "Schedutil" governor in Linux 4.7 the P-State comparison results on this Git kernel looked particularly terrible. I've since done some P-State tests on the same system using the Linux 4.5 and 4.6 kernels that further point towards a regression having taken place.

At least for this Intel Xeon E5-268W v3 system, the P-State CPU frequency scaling driver has become a lot worse since Linux 4.5 while the recent CPUFreq Linux 4.7 results show no issues there -- thus making it look like it's a problem with P-State on recent kernels itself as opposed to a regression elsewhere.

I ran 4.5, 4.6, and 4.7 kernel benchmarks with the P-State powersave and performance governors on this same system.

4.7 is surely much slower than 4.6~4.5 while the performance governor showed it regressing in 4.6 rather than 4.7.

The performance is surely a lot slower for this Xeon E5 system on Linux 4.6~4.7 with P-State. Again, CPUFreq on Linux 4.7 delivers the more optimal results -- in line with P-State from Linux 4.5.


You can dig through more of these P-State Linux 4.5/4.6/4.7 results via this OpenBenchmarking.org result file. I don't have any more information at this time nor have I had a chance yet to do similar tests yet on other Intel hardware to see how isolated or not this apparent P-State regression is besides on this Xeon E5 system. If there's enough interest, I'll fire up Phoromatic and tell it to auto-bisect this performance regression.

Stay tuned.
About The Author
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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 10,000 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 or contacted via MichaelLarabel.com.

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