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Message-ID: <CAJZ5v0gBUMXs=oANZRuOO7uUVdSD-n1inwYsoLr5or=2gEa2Mg@mail.gmail.com>
Date: Thu, 17 Jun 2021 15:33:19 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Rafael Wysocki <rjw@...ysocki.net>,
Ionela Voinescu <ionela.voinescu@....com>,
Jonathan Corbet <corbet@....net>,
Linux PM <linux-pm@...r.kernel.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Qian Cai <quic_qiancai@...cinc.com>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/3] cpufreq: Add start_cpu() and stop_cpu() callbacks
On Wed, Jun 16, 2021 at 8:48 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On CPU hot-unplug, the cpufreq core doesn't call any driver specific
> callback unless all the CPUs of a policy went away, in which case we
> call stop_cpu() callback.
>
> For the CPPC cpufreq driver, we need to perform per-cpu init/exit work
> which that can't be performed from policy specific init()/exit()
> callbacks.
>
> This patch adds a new callback, start_cpu() and modifies the stop_cpu()
> callback, to perform such CPU specific work.
>
> These routines are called whenever a CPU is added or removed from a
> policy.
>
> Note that this also moves the setting of policy->cpus to online CPUs
> only, outside of rwsem as we needed to call start_cpu() for online CPUs
> only. This shouldn't have any side effects.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> Documentation/cpu-freq/cpu-drivers.rst | 7 +++++--
> drivers/cpufreq/cpufreq.c | 19 +++++++++++++++----
> include/linux/cpufreq.h | 5 ++++-
> 3 files changed, 24 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/cpu-freq/cpu-drivers.rst b/Documentation/cpu-freq/cpu-drivers.rst
> index a697278ce190..15cfe42b4075 100644
> --- a/Documentation/cpu-freq/cpu-drivers.rst
> +++ b/Documentation/cpu-freq/cpu-drivers.rst
> @@ -71,8 +71,11 @@ And optionally
> .exit - A pointer to a per-policy cleanup function called during
> CPU_POST_DEAD phase of cpu hotplug process.
>
> - .stop_cpu - A pointer to a per-policy stop function called during
> - CPU_DOWN_PREPARE phase of cpu hotplug process.
> + .start_cpu - A pointer to a per-policy per-cpu start function called
> + during CPU online phase.
> +
> + .stop_cpu - A pointer to a per-policy per-cpu stop function called
> + during CPU offline phase.
>
> .suspend - A pointer to a per-policy suspend function which is called
> with interrupts disabled and _after_ the governor is stopped for the
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 802abc925b2a..128dfb1b0cdf 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1119,6 +1119,10 @@ static int cpufreq_add_policy_cpu(struct cpufreq_policy *policy, unsigned int cp
>
> cpumask_set_cpu(cpu, policy->cpus);
>
> + /* Do CPU specific initialization if required */
> + if (cpufreq_driver->start_cpu)
> + cpufreq_driver->start_cpu(policy, cpu);
> +
> if (has_target()) {
> ret = cpufreq_start_governor(policy);
> if (ret)
> @@ -1375,13 +1379,19 @@ static int cpufreq_online(unsigned int cpu)
> cpumask_copy(policy->related_cpus, policy->cpus);
> }
>
> - down_write(&policy->rwsem);
> /*
> * affected cpus must always be the one, which are online. We aren't
> * managing offline cpus here.
> */
> cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);
>
> + /* Do CPU specific initialization if required */
> + if (cpufreq_driver->start_cpu) {
> + for_each_cpu(j, policy->cpus)
> + cpufreq_driver->start_cpu(policy, j);
> + }
> +
> + down_write(&policy->rwsem);
> if (new_policy) {
> for_each_cpu(j, policy->related_cpus) {
> per_cpu(cpufreq_cpu_data, j) = policy;
> @@ -1581,6 +1591,10 @@ static int cpufreq_offline(unsigned int cpu)
> policy->cpu = cpumask_any(policy->cpus);
> }
>
> + /* Do CPU specific de-initialization if required */
> + if (cpufreq_driver->stop_cpu)
> + cpufreq_driver->stop_cpu(policy, cpu);
> +
> /* Start governor again for active policy */
> if (!policy_is_inactive(policy)) {
> if (has_target()) {
> @@ -1597,9 +1611,6 @@ static int cpufreq_offline(unsigned int cpu)
> policy->cdev = NULL;
> }
>
> - if (cpufreq_driver->stop_cpu)
> - cpufreq_driver->stop_cpu(policy);
> -
This should be a separate patch IMO, after you've migrated everyone to
->offline/->exit.
BTW, IMO it might be better to migrate ->stop_cpu to ->offline rather
than to ->exit.
> if (has_target())
> cpufreq_exit_governor(policy);
>
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index 353969c7acd3..c281b3df4e2f 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -371,7 +371,10 @@ struct cpufreq_driver {
> int (*online)(struct cpufreq_policy *policy);
> int (*offline)(struct cpufreq_policy *policy);
> int (*exit)(struct cpufreq_policy *policy);
> - void (*stop_cpu)(struct cpufreq_policy *policy);
> +
> + /* CPU specific start/stop */
> + void (*start_cpu)(struct cpufreq_policy *policy, unsigned int cpu);
> + void (*stop_cpu)(struct cpufreq_policy *policy, unsigned int cpu);
> int (*suspend)(struct cpufreq_policy *policy);
> int (*resume)(struct cpufreq_policy *policy);
>
> --
> 2.31.1.272.g89b43f80a514
>
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