Re: [PATCH V4 3/3] arm64: topology: Make AMUs work with modular cpufreq drivers

[Ionela Voinescu <ionela.voinescu@arm.com>]

On Friday 08 Jan 2021 at 16:46:53 (+0530), Viresh Kumar wrote:
> The AMU counters won't get used today if the cpufreq driver is built as
> a module as the amu core requires everything to be ready by late init.
> 
> Fix that properly by registering for cpufreq policy notifier. Note that
> the amu core don't have any cpufreq dependency after the first time
> CPUFREQ_CREATE_POLICY notifier is called for all the CPUs. And so we
> don't need to do anything on the CPUFREQ_REMOVE_POLICY notifier. And for
> the same reason we check if the CPUs are already parsed in the beginning
> of amu_fie_setup() and skip if that is true. Alternatively we can shoot
> a work from there to unregister the notifier instead, but that seemed
> too much instead of this simple check.
> 
> While at it, convert the print message to pr_debug instead of pr_info.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> 
> ---
>  arch/arm64/kernel/topology.c | 92 +++++++++++++++++++-----------------
>  1 file changed, 48 insertions(+), 44 deletions(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 57267d694495..e08a4126453a 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -199,69 +199,38 @@ static int freq_inv_set_max_ratio(int cpu, u64 max_rate, u64 ref_rate)
>  	return 0;
>  }
>  
> -static inline void
> -enable_policy_freq_counters(int cpu, cpumask_var_t valid_cpus)
> -{
> -	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
> -
> -	if (!policy) {
> -		pr_debug("CPU%d: No cpufreq policy found.\n", cpu);
> -		return;
> -	}
> -
> -	if (cpumask_subset(policy->related_cpus, valid_cpus))
> -		cpumask_or(amu_fie_cpus, policy->related_cpus,
> -			   amu_fie_cpus);
> -
> -	cpufreq_cpu_put(policy);
> -}
> -
>  static DEFINE_STATIC_KEY_FALSE(amu_fie_key);
>  #define amu_freq_invariant() static_branch_unlikely(&amu_fie_key)
>  
> -static int __init init_amu_fie(void)
> +static void amu_fie_setup(const struct cpumask *cpus)
>  {
> -	cpumask_var_t valid_cpus;
>  	bool invariant;
> -	int ret = 0;
>  	int cpu;
>  
> -	if (!zalloc_cpumask_var(&valid_cpus, GFP_KERNEL))
> -		return -ENOMEM;
> -
> -	if (!zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL)) {
> -		ret = -ENOMEM;
> -		goto free_valid_mask;
> -	}
> +	/* We are already set since the last insmod of cpufreq driver */
> +	if (unlikely(cpumask_subset(cpus, amu_fie_cpus)))
> +		return;
>  
> -	for_each_present_cpu(cpu) {
> +	for_each_cpu(cpu, cpus) {
>  		if (!freq_counters_valid(cpu) ||
>  		    freq_inv_set_max_ratio(cpu,
>  					   cpufreq_get_hw_max_freq(cpu) * 1000,
>  					   arch_timer_get_rate()))
> -			continue;
> -
> -		cpumask_set_cpu(cpu, valid_cpus);
> -		enable_policy_freq_counters(cpu, valid_cpus);
> +			return;
>  	}
>  
> -	/* Overwrite amu_fie_cpus if all CPUs support AMU */
> -	if (cpumask_equal(valid_cpus, cpu_present_mask))
> -		cpumask_copy(amu_fie_cpus, cpu_present_mask);
> -
> -	if (cpumask_empty(amu_fie_cpus))
> -		goto free_valid_mask;
> +	cpumask_or(amu_fie_cpus, amu_fie_cpus, cpus);
>  
>  	invariant = topology_scale_freq_invariant();
>  
>  	/* We aren't fully invariant yet */
>  	if (!invariant && !cpumask_equal(amu_fie_cpus, cpu_present_mask))
> -		goto free_valid_mask;
> +		return;
>  
>  	static_branch_enable(&amu_fie_key);
>  
> -	pr_info("CPUs[%*pbl]: counters will be used for FIE.",
> -		cpumask_pr_args(amu_fie_cpus));
> +	pr_debug("CPUs[%*pbl]: counters will be used for FIE.",
> +		 cpumask_pr_args(cpus));
>  
>  	/*
>  	 * Task scheduler behavior depends on frequency invariance support,
> @@ -271,13 +240,48 @@ static int __init init_amu_fie(void)
>  	 */
>  	if (!invariant)
>  		rebuild_sched_domains_energy();
> +}
> +
> +static int init_amu_fie_callback(struct notifier_block *nb, unsigned long val,
> +				 void *data)
> +{
> +	struct cpufreq_policy *policy = data;
> +
> +	if (val == CPUFREQ_CREATE_POLICY)
> +		amu_fie_setup(policy->related_cpus);
> +
> +	/*
> +	 * We don't need to handle CPUFREQ_REMOVE_POLICY event as the AMU
> +	 * counters don't have any dependency on cpufreq driver once we have
> +	 * initialized AMU support and enabled invariance. The AMU counters will
> +	 * keep on working just fine in the absence of the cpufreq driver, and
> +	 * for the CPUs for which there are no counters available, the last set
> +	 * value of freq_scale will remain valid as that is the frequency those
> +	 * CPUs are running at.
> +	 */
> +
> +	return 0;
> +}
> +
> +static struct notifier_block init_amu_fie_notifier = {
> +	.notifier_call = init_amu_fie_callback,
> +};
> +
> +static int __init init_amu_fie(void)
> +{
> +	int ret;
> +
> +	if (!zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL))
> +		return -ENOMEM;
>  
> -free_valid_mask:
> -	free_cpumask_var(valid_cpus);
> +	ret = cpufreq_register_notifier(&init_amu_fie_notifier,
> +					CPUFREQ_POLICY_NOTIFIER);
> +	if (ret)
> +		free_cpumask_var(amu_fie_cpus);
>  
>  	return ret;
>  }
> -late_initcall_sync(init_amu_fie);
> +core_initcall(init_amu_fie);
>  
>  bool arch_freq_counters_available(const struct cpumask *cpus)
>  {
> -- 
> 2.25.0.rc1.19.g042ed3e048af
> 

Reviewed-by: Ionela Voinescu <ionela.voinescu@arm.com>

Thanks,
Ionela.