linux-kernel - Re: [PATCH v2 3/4] cpufreq: Add strict_target to struct cpufreq

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Message-ID: <CAJZ5v0i10hF-41OH7AUzgWwyWSgV_PObN=t1bGSS930dENw5uw@mail.gmail.com>
Date:   Tue, 10 Nov 2020 13:37:41 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Zhang Rui <rui.zhang@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Doug Smythies <dsmythies@...us.net>
Subject: Re: [PATCH v2 3/4] cpufreq: Add strict_target to struct cpufreq_policy

On Tue, Nov 10, 2020 at 3:47 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 09-11-20, 17:53, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > Add a new field to be set when the CPUFREQ_GOV_FLAG_STRICT_TARGET
> > flag is set for the current governor to struct cpufreq_policy, so
> > that the drivers needing to check CPUFREQ_GOV_FLAG_STRICT_TARGET do
> > not have to access the governor object during every frequency
> > transition.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> >  drivers/cpufreq/cpufreq.c |    2 ++
> >  include/linux/cpufreq.h   |    6 ++++++
> >  2 files changed, 8 insertions(+)
> >
> > Index: linux-pm/drivers/cpufreq/cpufreq.c
> > ===================================================================
> > --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> > +++ linux-pm/drivers/cpufreq/cpufreq.c
> > @@ -2280,6 +2280,8 @@ static int cpufreq_init_governor(struct
> >               }
> >       }
> >
> > +     policy->strict_target = !!(policy->governor->flags & CPUFREQ_GOV_FLAG_STRICT_TARGET);
> > +
> >       return 0;
> >  }
> >
> > Index: linux-pm/include/linux/cpufreq.h
> > ===================================================================
> > --- linux-pm.orig/include/linux/cpufreq.h
> > +++ linux-pm/include/linux/cpufreq.h
> > @@ -109,6 +109,12 @@ struct cpufreq_policy {
> >       bool                    fast_switch_enabled;
> >
> >       /*
> > +      * Set if the CPUFREQ_GOV_FLAG_STRICT_TARGET flag is set for the
> > +      * current governor.
> > +      */
> > +     bool                    strict_target;
> > +
> > +     /*
> >        * Preferred average time interval between consecutive invocations of
> >        * the driver to set the frequency for this policy.  To be set by the
> >        * scaling driver (0, which is the default, means no preference).
>
> I was kind of hoping to avoid adding a field here when I proposed updating the
> gov structure. I do understand the performance related penalty of accessing the
> gov structure for fast switch case though and so wonder if we really need this,
> then should we avoid changing the gov structure at all ? I mean there is only
> one user of that field now, do we really need a flag for it ? We can just do the
> string comparison here with powersave and performance to set strict_target.
>
> Whatever you feel is better though.

The cost of having the flag is zero and it allows things to be
documented a bit better IMV.

> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

Thanks!