linux-kernel - Re: [PATCH] cpufreq: conservative: Take limits changes into account properly

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Date:   Tue, 16 Oct 2018 08:38:49 +0200
From:   Waldemar Rymarkiewicz <waldemar.rymarkiewicz@...il.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     linux-pm@...r.kernel.org, Viresh Kumar <viresh.kumar@...aro.org>,
        Waldemar Rymarkiewicz <waldemarx.rymarkiewicz@...el.com>,
        linux-kernel@...r.kernel.org,
        "Bartholomae, Thomas" <t.bartholomae@...el.com>
Subject: Re: [PATCH] cpufreq: conservative: Take limits changes into account properly

On Mon, 15 Oct 2018 at 23:24, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> If the policy limits change between invocations of cs_dbs_update(),
> the requested frequency value stored in dbs_info may not be updated
> and the function may use a stale value of it next time.  Moreover, if
> idle periods are takem into account by cs_dbs_update(), the requested
> frequency value stored in dbs_info may be below the min policy limit,
> which is incorrect.
>
> To fix these problems, always update the requested frequency value
> in dbs_info along with the local copy of it when the previous
> requested frequency is beyond the policy limits and avoid decreasing
> the requested frequency below the min policy limit when taking
> idle periods into account.
>
> Reported-by: Waldemar Rymarkiewicz <waldemarx.rymarkiewicz@...el.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpufreq/cpufreq_conservative.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> Index: linux-pm/drivers/cpufreq/cpufreq_conservative.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq_conservative.c
> +++ linux-pm/drivers/cpufreq/cpufreq_conservative.c
> @@ -80,8 +80,10 @@ static unsigned int cs_dbs_update(struct
>          * changed in the meantime, so fall back to current frequency in that
>          * case.
>          */
> -       if (requested_freq > policy->max || requested_freq < policy->min)
> +       if (requested_freq > policy->max || requested_freq < policy->min) {
>                 requested_freq = policy->cur;
> +               dbs_info->requested_freq = requested_freq;
> +       }
>
>         freq_step = get_freq_step(cs_tuners, policy);
>
> @@ -92,7 +94,7 @@ static unsigned int cs_dbs_update(struct
>         if (policy_dbs->idle_periods < UINT_MAX) {
>                 unsigned int freq_steps = policy_dbs->idle_periods * freq_step;
>
> -               if (requested_freq > freq_steps)
> +               if (requested_freq > policy->min + freq_steps)
>                         requested_freq -= freq_steps;
>                 else
>                         requested_freq = policy->min;

Looks good.

Acked-by: Waldemar Rymarkiewicz <waldemarx.rymarkiewicz@...el.com>