linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Override parameters if HWP forced by BIOS

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Date:   Thu, 9 Sep 2021 19:22:19 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <len.brown@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: intel_pstate: Override parameters if HWP forced
 by BIOS

On Thu, Sep 9, 2021 at 6:12 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Sep 9, 2021 at 3:20 PM Doug Smythies <dsmythies@...us.net> wrote:
> >
> > On Thu, Sep 9, 2021 at 4:18 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > >
> > > On Thu, Sep 9, 2021 at 8:52 AM Srinivas Pandruvada
> > > <srinivas.pandruvada@...ux.intel.com> wrote:
> > > >
> > > > On Wed, 2021-09-08 at 20:48 -0700, Doug Smythies wrote:
> > > > > If HWP has been already been enabled by BIOS, it may be
> > > > > necessary to override some kernel command line parameters.
> > > > > Once it has been enabled it requires a reset to be disabled.
> > > > >
> > > > > Signed-off-by: Doug Smythies <dsmythies@...us.net>
> > > > > ---
> > > > >  drivers/cpufreq/intel_pstate.c | 22 ++++++++++++++++------
> > > > >  1 file changed, 16 insertions(+), 6 deletions(-)
> > > > >
> > > > > diff --git a/drivers/cpufreq/intel_pstate.c
> > > > > b/drivers/cpufreq/intel_pstate.c
> > > > > index bb4549959b11..073bae5d4498 100644
> > > > > --- a/drivers/cpufreq/intel_pstate.c
> > > > > +++ b/drivers/cpufreq/intel_pstate.c
> > > > > @@ -3267,7 +3267,7 @@ static int __init intel_pstate_init(void)
> > > > >                  */
> > > > >                 if ((!no_hwp && boot_cpu_has(X86_FEATURE_HWP_EPP)) ||
> > > > >                     intel_pstate_hwp_is_enabled()) {
> > > > > -                       hwp_active++;
> > > > > +                       hwp_active = 1;
> > > > Why this change?
> > >
> > > I think hwp_active can be changed to bool and then it would make sense
> > > to update this line.
> > >
> > > > >                         hwp_mode_bdw = id->driver_data;
> > > > >                         intel_pstate.attr = hwp_cpufreq_attrs;
> > > > >                         intel_cpufreq.attr = hwp_cpufreq_attrs;
> > > > > @@ -3347,17 +3347,27 @@ device_initcall(intel_pstate_init);
> > > > >
> > > > >  static int __init intel_pstate_setup(char *str)
> > > > >  {
> > > > > +       /*
> > > > > +        * If BIOS is forcing HWP, then parameter
> > > > > +        * overrides might be needed. Only print
> > > > > +        * the message once, and regardless of
> > > > > +        * any overrides.
> > > > > +        */
> > > > > +       if(!hwp_active
> > > > This part of code is from early_param, Is it possible that
> > > > hwp_active is not 0?
> > >
> > > Well, it wouldn't matter even if it were nonzero.  This check is just
> > > pointless anyway.
> > >
> > > > > && boot_cpu_has(X86_FEATURE_HWP))
> > > > > +               if(intel_pstate_hwp_is_enabled()){
> > >
> > > This should be
> > >
> > > if (boot_cpu_has(X86_FEATURE_HWP) && intel_pstate_hwp_is_enabled()) {
> >
> > Disagree.
> > This routine gets executed once per intel_pstate related grub command
> > line entry. The purpose of the "if(!hwp_active" part is to prevent the
> > printing of the message to the logs multiple times.
>
> Ah OK.  Fair enough.
>
> You can do all of the checks in one conditional, though.  They will be
> processed left-to-right anyway.
>
> But then it would be good to avoid calling
> intel_pstate_hwp_is_enabled() multiple times if it returns false.
>
> And having said all that I'm not sure why you are trying to make
> no_hwp depend on !hwp_active?  I will not be taken into account anyway
> if intel_pstate_hwp_is_enabled() returns 'true'?
>
> So if no_hwp is covered regardless, you may move the
> intel_pstate_hwp_is_enabled() inside the no_load conditional.
>
> Alternatively, and I would do that, intel_pstate_hwp_is_enabled()
> could be evaluated earlier in intel_pstate_init() and if it returned
> 'true', both no_load and no_hwp would be disregarded.

Something like the attached, for the record.

View attachment "intel_pstate-arguments.patch" of type "text/x-patch" (1463 bytes)