linux-kernel - Re: problem in changing from active to passive mode

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Message-ID: <CAJZ5v0ij105B05xPGgfauwFv1KhXRnwh5p28R1y11qKWjxUOhg@mail.gmail.com>
Date:   Thu, 28 Oct 2021 19:57:09 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Julia Lawall <julia.lawall@...ia.fr>
Cc:     Doug Smythies <dsmythies@...us.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: problem in changing from active to passive mode

On Thu, Oct 28, 2021 at 7:29 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Oct 28, 2021 at 7:10 PM Julia Lawall <julia.lawall@...ia.fr> wrote:
> >
> > > Now, for your graph 3, are you saying this pseudo
> > > code of the process is repeatable?:
> > >
> > > Power up the system, booting kernel 5.9
> > > switch to passive/schedutil.
> > > wait X minutes for system to settle
> > > do benchmark, result ~13 seconds
> > > re-boot to kernel 5.15-RC
> > > switch to passive/schedutil.
> > > wait X minutes for system to settle
> > > do benchmark, result ~40 seconds
> > > re-boot to kernel 5.9
> > > switch to passive/schedutil.
> > > wait X minutes for system to settle
> > > do benchmark, result ~28 seconds
> >
> > In the first boot of 5.9, the des (desired?) field of the HWP_REQUEST
> > register is 0 and in the second boot (after booting 5.15 and entering
> > passive mode) it is 10.  I don't know though if this is a bug or a
> > feature...
>
> It looks like a bug.
>
> I think that the desired value is not cleared on driver exit which
> should happen.  Let me see if I can do a quick patch for that.

Please check the behavior with the attached patch applied.

View attachment "intel_pstate-clear-desired-on-offline.patch" of type "text/x-patch" (611 bytes)