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

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Date:	Tue, 2 Feb 2016 10:33:11 +0000
From:	"Longepe, Philippe" <philippe.longepe@...el.com>
To:	Thomas Voegtle <tv@...96.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Gasparini, Stephane" <stephane.gasparini@...el.com>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>
Subject: RE: Performance drop on Baytrail with 4.5-rc2

Hi Thomas,

Yes, this new algorithm is intented to improve the performance versus power efficiency.

Can you please provide us the exact instructions to reproduce your test ?

Best Regards,

Philippe,

________________________________________
From: Thomas Voegtle [tv@...96.de]
Sent: Monday, February 01, 2016 9:34 PM
To: Longepe, Philippe
Cc: linux-kernel@...r.kernel.org; Gasparini, Stephane; Wysocki, Rafael J
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

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