linux-kernel - Re: [PATCH v2] cpufreq: Replace pointer subtraction with iteration macros

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Message-ID: <CAJZ5v0gp61N2e1VkPzJQtgXm-DTiP1TASoy=v9mWrP=CcybmJA@mail.gmail.com>
Date: Tue, 23 Sep 2025 17:21:51 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Dhruva Gole <d-gole@...com>, Zihuan Zhang <zhangzihuan@...inos.cn>
Cc: Viresh Kumar <viresh.kumar@...aro.org>, zhenglifeng <zhenglifeng1@...wei.com>, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cpufreq: Replace pointer subtraction with iteration macros

On Tue, Sep 23, 2025 at 11:09 AM Dhruva Gole <d-gole@...com> wrote:
>
> On Sep 23, 2025 at 15:55:53 +0800, Zihuan Zhang wrote:
> > The cpufreq documentation suggests avoiding direct pointer subtraction
> > when working with entries in driver_freq_table, as it is relatively
> > costly. Instead, the recommended approach is to use the provided
> > iteration macros:
>
> Thanks for the patch,
> Just say "macro" not "macros".
>
> >
> > - cpufreq_for_each_valid_entry_idx()
> >
> > Replace pointer subtraction in freq_table.c with the macros
> > cpufreq_for_each_entry_idx() and cpufreq_for_each_valid_entry_idx(), as
>
> Where is "cpufreq_for_each_entry_idx" in this entire patch?
> Please drop this reference, why confuse people?
>
> > the index does not need initialization, avoiding unnecessary
> > computation. This improves code clarity and follows the established
> > cpufreq coding style.
>
> You don't need to add all this to the commit message about the
> unnecessary computation, code clarity, etc..
> Please keep it to the point.
>
> >
> > No functional change intended.
> >
> > Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>
> >
> > V2:
> >  - Remove unnecessary initialization for current and remaining follow Rafael's suggestion
>
> You didn't fix Rafael's first comment [1] about the $subject, and also please
> add links to previous revisions for ease of review.
>
> [1] > In the subject, this is just one macro, not multiple macros.

@Dhruva, thanks for the review!

I've fixed up the shortcomings pointed out above and applied the patch
as 6.18 material.

> > ---
> >  drivers/cpufreq/freq_table.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/cpufreq/freq_table.c b/drivers/cpufreq/freq_table.c
> > index d5111ee56e38..408fd8fee2e3 100644
> > --- a/drivers/cpufreq/freq_table.c
> > +++ b/drivers/cpufreq/freq_table.c
> > @@ -33,16 +33,17 @@ int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy)
> >       struct cpufreq_frequency_table *pos, *table = policy->freq_table;
> >       unsigned int min_freq = ~0;
> >       unsigned int max_freq = 0;
> > +     unsigned int i;
> >       unsigned int freq;
> >
> > -     cpufreq_for_each_valid_entry(pos, table) {
> > +     cpufreq_for_each_valid_entry_idx(pos, table, i) {
> >               freq = pos->frequency;
> >
> >               if ((!cpufreq_boost_enabled() || !policy->boost_enabled)
> >                   && (pos->flags & CPUFREQ_BOOST_FREQ))
> >                       continue;
> >
> > -             pr_debug("table entry %u: %u kHz\n", (int)(pos - table), freq);
> > +             pr_debug("table entry %u: %u kHz\n", i, freq);
> >               if (freq < min_freq)
> >                       min_freq = freq;
> >               if (freq > max_freq)
> > @@ -126,7 +127,7 @@ int cpufreq_table_index_unsorted(struct cpufreq_policy *policy,
> >       };
> >       struct cpufreq_frequency_table *pos;
> >       struct cpufreq_frequency_table *table = policy->freq_table;
> > -     unsigned int freq, diff, i = 0;
> > +     unsigned int freq, diff, i;
> >       int index;
>
> Usually, it isn't advised to touch code that's not strictly relevant to
> your patch. However since this seems like a minor fixup it's fine by
> me... Upto Rafael whether he prefers to have/not have this unrelated change.
>
> But atleast mention in your commit message that you're also removing the
> initialization from cpufreq_table_index_unsorted as part of some minor cleanup
> (which seems kinda unnecessary to me TBH in the first place)

Yeah, better to say about things like this in the patch changelog.
I've fixed that too.