linux-kernel - Re: 5.2-rc2: low framerate in flightgear, cpu not running at full speed, thermal related?

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Message-ID: <CAJZ5v0j2pb2WxSA+S44Mr-6bpOx-P9A_T2-sDG3CiWSqLMg3sA@mail.gmail.com>
Date:   Wed, 12 Jun 2019 23:44:30 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Doug Smythies <dsmythies@...us.net>, Pavel Machek <pavel@....cz>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: 5.2-rc2: low framerate in flightgear, cpu not running at full
 speed, thermal related?

On Wed, Jun 12, 2019 at 4:45 AM Doug Smythies <dsmythies@...us.net> wrote:
>
> Hi,
>
> So, currently there seems to be 3 issues in this thread
> (and I am guessing a little, without definitive data):
>
> 1.) On your system Kernel 5.4-rc2 (or 4) defaults to the intel_pstate CPU frequency
> scaling driver and the powersave governor, but kernel 4.6 defaults to the
> acpi-cpufreq CPU frequency scaling driver and the ondemand governor.

Which means that intel_pstate works in the active mode by default and
so it uses its internal governor.

That governor is more performance-oriented than ondemand and it very
well may cause more power to be allocated for the processor - at the
expense of the GPU.

The lower-than-expected frame rate may result from that, in principle.

One way to mitigate that might be to use intel_pstate in the passive
mode (pass intel_pstate=passive to the kernel in the command line)
along with either ondemand or schedutil as the governor.