linux-kernel - Re: [PATCH] cpufreq: stats: Improve the performance of cpufreq_stats_create

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Message-ID: <CAJZ5v0iyLmT=V1rSehkSaO7Yzn0RG53vdBQ-+R0tM-HZg1xE-Q@mail.gmail.com>
Date:   Mon, 21 Aug 2023 21:00:24 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Dhruva Gole <d-gole@...com>, Liao Chang <liaochang1@...wei.com>
Cc:     viresh.kumar@...aro.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: stats: Improve the performance of cpufreq_stats_create_table()

On Mon, Aug 21, 2023 at 11:14 AM Dhruva Gole <d-gole@...com> wrote:
>
> On Aug 18, 2023 at 09:50:00 +0000, Liao Chang wrote:
> > In the worst case, the freq_table of policy data is not sorted and
> > contains duplicate frequencies, this means that it needs to iterate
> > through the entire freq_table of policy to ensure each frequency is
> > unique in the freq_table of stats data, this has a time complexity of
> > O(N^2), where N is the number of frequencies in the freq_table of
> > policy.
> >
> > However, if the policy.freq_table is already sorted and contains no
> > duplicate frequencices, it can reduce the time complexity of creating
>
> s/frequencices/frequencies?

I've fixed this when applying the patch.

> > stats.freq_table to O(N), the 'freq_table_sorted' field of policy data
> > can be used to indicate whether the policy.freq_table is sorted.
> >
> > Signed-off-by: Liao Chang <liaochang1@...wei.com>
> > ---
> >  drivers/cpufreq/cpufreq_stats.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
> > index 55c7ffd37d1c..fcb74050711a 100644
> > --- a/drivers/cpufreq/cpufreq_stats.c
> > +++ b/drivers/cpufreq/cpufreq_stats.c
> > @@ -243,7 +243,8 @@ void cpufreq_stats_create_table(struct cpufreq_policy *policy)
> >
> >       /* Find valid-unique entries */
> >       cpufreq_for_each_valid_entry(pos, policy->freq_table)
> > -             if (freq_table_get_index(stats, pos->frequency) == -1)
> > +             if ((policy->freq_table_sorted != CPUFREQ_TABLE_UNSORTED) ||

I've also removed the redundant parens from this check.

>
> [...]
>
> Otherwise looks okay to me,
>
> Reviewed-by: Dhruva Gole <d-gole@...com>

Applied as 6.6 material (with the changes mentioned above), thanks!