linux-kernel - Re: [RFT][PATCH v1 2/8] cpufreq/sched: Move cpufreq-specific EAS checks to cpufreq

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Message-ID: <f792b69d-28b3-48a7-8bc2-cea6f35bd19e@arm.com>
Date: Thu, 17 Apr 2025 13:28:04 +0100
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>,
 Peter Zijlstra <peterz@...radead.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Morten Rasmussen <morten.rasmussen@....com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
 Pierre Gondois <pierre.gondois@....com>
Subject: Re: [RFT][PATCH v1 2/8] cpufreq/sched: Move cpufreq-specific EAS
 checks to cpufreq

On 4/16/25 18:59, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Doing cpufreq-specific EAS checks that require accessing policy
> internals directly from sched_is_eas_possible() is a bit unfortunate,
> so introduce cpufreq_ready_for_eas() in cpufreq, move those checks
> into that new function and make sched_is_eas_possible() call it.
> 
> While at it, address a possible race between the EAS governor check
> and governor change by doing the former under the policy rwsem.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> v0.3 -> v1
>      * Add a new helper called cpufreq_policy_is_good_for_eas() which is
>        properly synchronized with governor changes.
>      * Slightly modify debug messages.
> 
> This patch is regarded as a cleanup for 6.16.
> 
> ---
>  drivers/cpufreq/cpufreq.c |   32 ++++++++++++++++++++++++++++++++
>  include/linux/cpufreq.h   |    2 ++
>  kernel/sched/topology.c   |   25 +++++--------------------
>  3 files changed, 39 insertions(+), 20 deletions(-)
> 
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -3041,6 +3041,38 @@
>  
>  	return 0;
>  }
> +
> +static bool cpufreq_policy_is_good_for_eas(unsigned int cpu)
> +{
> +	struct cpufreq_policy *policy __free(put_cpufreq_policy);
> +
> +	policy = cpufreq_cpu_get(cpu);
> +	if (!policy) {
> +		pr_debug("cpufreq policy not set for CPU: %d", cpu);
> +		return false;
> +	}
> +
> +	guard(cpufreq_policy_read)(policy);
> +
> +	return sugov_is_governor(policy);
> +}
> +
> +bool cpufreq_ready_for_eas(const struct cpumask *cpu_mask)
> +{
> +	unsigned int cpu;
> +
> +	/* Do not attempt EAS if schedutil is not being used. */
> +	for_each_cpu(cpu, cpu_mask) {
> +		if (!cpufreq_policy_is_good_for_eas(cpu)) {
> +			pr_debug("rd %*pbl: schedutil is mandatory for EAS\n",
> +				 cpumask_pr_args(cpu_mask));
> +			return false;
> +		}
> +	}
> +
> +	return true;
> +}
> +
>  module_param(off, int, 0444);
>  module_param_string(default_governor, default_governor, CPUFREQ_NAME_LEN, 0444);
>  core_initcall(cpufreq_core_init);
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -1212,6 +1212,8 @@
>  		struct cpufreq_frequency_table *table,
>  		unsigned int transition_latency);
>  
> +bool cpufreq_ready_for_eas(const struct cpumask *cpu_mask);
> +
>  static inline void cpufreq_register_em_with_opp(struct cpufreq_policy *policy)
>  {
>  	dev_pm_opp_of_register_em(get_cpu_device(policy->cpu),
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -212,8 +212,6 @@
>  static bool sched_is_eas_possible(const struct cpumask *cpu_mask)
>  {
>  	bool any_asym_capacity = false;
> -	struct cpufreq_policy *policy;
> -	bool policy_is_ready;
>  	int i;
>  
>  	/* EAS is enabled for asymmetric CPU capacity topologies. */
> @@ -248,25 +246,12 @@
>  		return false;
>  	}
>  
> -	/* Do not attempt EAS if schedutil is not being used. */
> -	for_each_cpu(i, cpu_mask) {
> -		policy = cpufreq_cpu_get(i);
> -		if (!policy) {
> -			if (sched_debug()) {
> -				pr_info("rd %*pbl: Checking EAS, cpufreq policy not set for CPU: %d",
> -					cpumask_pr_args(cpu_mask), i);
> -			}
> -			return false;
> -		}
> -		policy_is_ready = sugov_is_governor(policy);
> -		cpufreq_cpu_put(policy);
> -		if (!policy_is_ready) {
> -			if (sched_debug()) {
> -				pr_info("rd %*pbl: Checking EAS, schedutil is mandatory\n",
> -					cpumask_pr_args(cpu_mask));
> -			}
> -			return false;
> +	if (!cpufreq_ready_for_eas(cpu_mask)) {
> +		if (sched_debug()) {
> +			pr_info("rd %*pbl: Checking EAS: cpufreq is not ready",

Missing \n here.
There is another one you touch, I've sent patches already last month:
https://lore.kernel.org/lkml/20250319131324.224228-1-christian.loehle@arm.com/

With that:
Reviewed-by: Christian Loehle <christian.loehle@....com>

> +				cpumask_pr_args(cpu_mask));
>  		}
> +		return false;
>  	}
>  
>  	return true;
> 
> 
>