linux-kernel - Performance drop on Baytrail with 4.5-rc2

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Date:	Mon, 1 Feb 2016 21:34:28 +0100 (CET)
From:	Thomas Voegtle <tv@...96.de>
To:	philippe.longepe@...el.com
cc:	linux-kernel@...r.kernel.org, stephane.gasparini@...el.com,
	rafael.j.wysocki@...el.com
Subject: Performance drop on Baytrail with 4.5-rc2

Hi,

I have a Celeron J1900 system (Asrock Q1900B-ITX) always running the
latest kernel.
Since running the 4.5-rc2 kernel I have a performance drop in a ffmpeg
benchmark compared to 4.4. Converting a piece of mpeg to mp4 (to
/dev/null).

4.1 made the benchmark in 74s, 4.4 in 75s and now the 4.5-rc2 in 80s.

As the benchmark is very stable in results I easily could bisest it down
to the commit:

commit e70eed2b64545ab5c9d2f4d43372d79762f1b985
Author: Philippe Longepe <philippe.longepe@...el.com>
Date:   Fri Dec 4 17:40:32 2015 +0100

     cpufreq: intel_pstate: Account for non C0 time

I can revert this commit on top on 4.5-rc2 (4 of 5 hunks) and then the
benchmark is down to 76s.

Was this intended to decrease energy consumption?

     Thomas