linux-kernel - Re: [PATCH V4 2/4] cpufreq: intel_pstate: Migrate to ->offline() instead of ->stop

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Date:   Wed, 23 Jun 2021 17:13:00 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 2/4] cpufreq: intel_pstate: Migrate to ->offline() instead of ->stop_cpu()

On Wednesday, June 23, 2021 6:24:40 AM CEST Viresh Kumar wrote:
> commit 367dc4aa932b ("cpufreq: Add stop CPU callback to cpufreq_driver
> interface") added the stop_cpu() callback to allow the drivers to do
> clean up before the CPU is completely down and its state can't be
> modified.
> 
> At that time the CPU hotplug framework used to call the cpufreq core's
> registered notifier for different events like CPU_DOWN_PREPARE and
> CPU_POST_DEAD. The stop_cpu() callback was called during the
> CPU_DOWN_PREPARE event.
> 
> This is no longer the case, cpuhp_cpufreq_offline() is called only once
> by the CPU hotplug core now and we don't really need to separately
> call stop_cpu() for cpufreq drivers.
> 
> Migrate to using the offline() callbacks instead of stop_cpu().
> 
> Cc: Dirk Brandewie <dirk.brandewie@...il.com>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/cpufreq/intel_pstate.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 0e69dffd5a76..b4c0ff7f5b71 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -2335,6 +2335,8 @@ static int intel_pstate_cpu_offline(struct cpufreq_policy *policy)
>  
>  	pr_debug("CPU %d going offline\n", cpu->cpu);
>  
> +	intel_pstate_clear_update_util_hook(policy->cpu);

As mentioned already in

https://lore.kernel.org/linux-pm/CAJZ5v0g2tCZptcqh+c55YYiO7rDHmZivMLsmpq_7005zNPN1xg@mail.gmail.com/

this isn't particularly clean, because intel_pstate_cpu_offline() is
also used in the passive mode where the above call is not needed.

I would make a change like in the patch below instead.

> +
>  	if (cpu->suspended)
>  		return 0;

---
From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Subject: [PATCH] cpufreq: intel_pstate: Combine ->stop_cpu() and ->offline()

Combine the ->stop_cpu() and ->offline() callback routines for the
active mode of intel_pstate so as to avoid setting the ->stop_cpu
callback pointer which is going to be dropped from the framework.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/cpufreq/intel_pstate.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -2577,11 +2577,13 @@ static int intel_pstate_cpu_online(struc
 	return 0;
 }
 
-static void intel_pstate_stop_cpu(struct cpufreq_policy *policy)
+static int intel_pstate_stop_cpu(struct cpufreq_policy *policy)
 {
 	pr_debug("CPU %d stopping\n", policy->cpu);
 
 	intel_pstate_clear_update_util_hook(policy->cpu);
+
+	return intel_pstate_cpu_offline(policy);
 }
 
 static int intel_pstate_cpu_exit(struct cpufreq_policy *policy)
@@ -2654,8 +2656,7 @@ static struct cpufreq_driver intel_pstat
 	.resume		= intel_pstate_resume,
 	.init		= intel_pstate_cpu_init,
 	.exit		= intel_pstate_cpu_exit,
-	.stop_cpu	= intel_pstate_stop_cpu,
-	.offline	= intel_pstate_cpu_offline,
+	.offline	= intel_pstate_stop_cpu,
 	.online		= intel_pstate_cpu_online,
 	.update_limits	= intel_pstate_update_limits,
 	.name		= "intel_pstate",