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

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Message-ID: <CAAYoRsUHQoFH4rb2cu5ZgMc8=e7WWZt8qQwZ6eFAtVSD1kghoA@mail.gmail.com>
Date:   Thu, 9 Sep 2021 21:11:46 -0700
From:   Doug Smythies <dsmythies@...us.net>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        dsmythies <dsmythies@...us.net>
Subject: Re: [PATCH] cpufreq: intel_pstate: Override parameters if HWP forced
 by BIOS

On Thu, Sep 9, 2021 at 7:53 AM Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:

> On Thu, 2021-09-09 at 06:30 -0700, Doug Smythies wrote:
> > On Wed, Sep 8, 2021 at 11:33 PM 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?
> >
> > It was just to keep it at 1, but I agree not absolutely needed.
> >
> > >
> > > >                         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?
> >
> > Not at this point, in any testing I did.
> > But I do not know the authoritative answer
> > to your question.
> >
> But as you explained you want to prevent repeated print of
> "HWP enabled by BIOS". So you need this.
>
> > >
> > > > && boot_cpu_has(X86_FEATURE_HWP))
> > > > +               if(intel_pstate_hwp_is_enabled()){
> > > > +                       pr_info("HWP enabled by BIOS\n");
> > > > +                       hwp_active = 1;
> > > > +               }
> > > >         if (!str)
> > > >                 return -EINVAL;
> > > >
> > > > -       if (!strcmp(str, "disable"))
> > > > +       if (!strcmp(str, "disable") && !hwp_active)
> > > >                 no_load = 1;
> > > > -       else if (!strcmp(str, "active"))
> > > > +       if (!strcmp(str, "active"))
> > > >                 default_driver = &intel_pstate;
> > > > -       else if (!strcmp(str, "passive"))
> > > > +       if (!strcmp(str, "passive"))
> > > >                 default_driver = &intel_cpufreq;
> > >
> > > Why "else if" changed to "if" ?
> >
> > Because it doesn't matter anyway and I would
> > have had to figure out another qualifier.
> > This way, and given that this executes once per
> > intel_pstate command line parameter, the code
> > executes the way it used to, overall.
> If someone specified intel_pstate=active, it will also compare with
> "passive" with this change.

Disagree.
As far as I can tell, and I tested, it works as expected.

... Doug

> > > > -
> > > > -       if (!strcmp(str, "no_hwp")) {
> > > > +       if (!strcmp(str, "no_hwp") && !hwp_active) {
> > > >                 pr_info("HWP disabled\n");
> > > >                 no_hwp = 1;
> > > >         }
> > >
> > >
>
>