linux-kernel - Re: Commit 554c8aa8ecad causing severe performance degression with pcc-cpufreq

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Date:   Tue, 17 Jul 2018 11:11:52 +0200
From:   Andreas Herrmann <aherrmann@...e.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Commit 554c8aa8ecad causing severe performance degression with
 pcc-cpufreq

On Tue, Jul 17, 2018 at 11:06:29AM +0200, Rafael J. Wysocki wrote:
> On Tue, Jul 17, 2018 at 10:50 AM, Andreas Herrmann <aherrmann@...e.com> wrote:
> 
> [cut]
> 
> >
> > On balance before this commit users could use pcc-cpufreq but had
> > already suboptimal performance (compared to say intel_pstate driver
> > which can be used changing BIOS options).
> 
> BTW, I wonder why you need to change the BIOS options for intel_pstate to load.

I think this is because of (in intel_pstate_init()):

        /*
         * The Intel pstate driver will be ignored if the platform
         * firmware has its own power management modes.
         */
        if (intel_pstate_platform_pwr_mgmt_exists())
                return -ENODEV;


> It should be initialized before pcc-cpufreq (according to their
> respective initcall levels), so in theory intel_pstate should be used
> by default on the affected systems anyway.

> What BIOS settings need to be changed for that?

Already answered in other mail.


Andreas