linux-kernel - Re: [PATCH v2] cpufreq: Avoid get

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Message-ID: <CAJZ5v0hj74fK3u6AN_zTKUAROogCiVySH3HnMxvyUg=P6xAdvA@mail.gmail.com>
Date: Tue, 19 Aug 2025 21:14:40 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "zhenglifeng (A)" <zhenglifeng1@...wei.com>, Zihuan Zhang <zhangzihuan@...inos.cn>, 
	Viresh Kumar <viresh.kumar@...aro.org>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cpufreq: Avoid get_governor() for first policy

On Fri, Jul 25, 2025 at 11:11 AM zhenglifeng (A)
<zhenglifeng1@...wei.com> wrote:
>
> On 2025/7/25 12:14, Zihuan Zhang wrote:
>
> > When a cpufreq driver registers the first policy, it may attempt to
> > initialize the policy governor from `last_governor`. However, this is
> > meaningless for the first policy instance, because `last_governor` is
> > only updated when policies are removed (e.g. during CPU offline).
> >
> > The `last_governor` mechanism is intended to restore the previously
> > used governor across CPU hotplug events. For the very first policy,
> > there is no "previous governor" to restore, so calling
> > get_governor(last_governor) is unnecessary and potentially confusing.
> >
> > This patch skips looking up `last_governor` when registering the first
> > policy. Instead, it directly uses the default governor after all
> > governors have been registered and are available.
> >
> > This avoids meaningless lookups, reduces unnecessary module reference
> > handling, and simplifies the initial policy path.
> >
> > Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>
> >
> > ---
> > Changes in v2:
> >  - Fix the case where the governor is NULL.
> > ---
> > ---
> >  drivers/cpufreq/cpufreq.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index d7426e1d8bdd..1aa559f53479 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -1122,7 +1122,8 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy)
> >
> >       if (has_target()) {
> >               /* Update policy governor to the one used before hotplug. */
> > -             gov = get_governor(policy->last_governor);
> > +             if (policy->last_governor[0] != '\0')
> > +                     gov = get_governor(policy->last_governor);
> >               if (gov) {
> >                       pr_debug("Restoring governor %s for cpu %d\n",
> >                                gov->name, policy->cpu);
>
> Reviewed-by: Lifeng Zheng <zhenglifeng1@...wei.com>

Applied as 6.18 material, thanks!