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

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Date:   Thu, 28 Oct 2021 19:29:12 +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 7:10 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.