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

From: Rafael J. Wysocki
Date: Wed Jun 23 2021 - 11:13:05 EST


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@xxxxxxxxx>
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxx/

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@xxxxxxxxx>
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@xxxxxxxxx>
---
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",