Subject: Re: [PATCH V3 1/2] topology: Allow multiple entities to provide sched_freq_tick() callback

From: Ionela Voinescu <[email-masked]>
Date: Wed, 17 Feb 2021 00:24:22 +0000

Hey,

On Friday 05 Feb 2021 at 14:44:24 (+0530), Viresh Kumar wrote:
> On 03-02-21, 11:45, Ionela Voinescu wrote:
> > Therefore, I think system level invariance management (checks and
> > call to rebuild_sched_domains_energy()) also needs to move from arm64
> > code to arch_topology code.
> 
> Here is the 3rd patch of this series then :)
> 

I think it could be merged in patch 1/2 as it's part of enabling the use
of multiple sources of information for FIE. Up to you!

> From: Viresh Kumar <[email-masked]>
> Date: Fri, 5 Feb 2021 13:31:53 +0530
> Subject: [PATCH] drivers: arch_topology: rebuild sched domains on invariance
>  change
> 
> We already do this for the arm64, move it to arch_topology.c as we
> manage all sched_freq_tick sources here now.
> 
> Reported-by: Ionela Voinescu <[email-masked]>
> Signed-off-by: Viresh Kumar <[email-masked]>
> ---
>  arch/arm64/kernel/topology.c | 16 ----------------
>  drivers/base/arch_topology.c | 22 ++++++++++++++++++++++
>  2 files changed, 22 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 1e47dfd465f8..47fca7376c93 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -240,7 +240,6 @@ static struct scale_freq_data amu_sfd = {
>  
>  static void amu_fie_setup(const struct cpumask *cpus)
>  {
> -	bool invariant;
>  	int cpu;
>  
>  	/* We are already set since the last insmod of cpufreq driver */
> @@ -257,25 +256,10 @@ static void amu_fie_setup(const struct cpumask *cpus)
>  
>  	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))
> -		return;
> -

You still need these checks, otherwise you could end up with only part
of the CPUs setting a scale factor, when only part of the CPUs support
AMUs and there is no cpufreq support for FIE.

>  	topology_set_scale_freq_source(&amu_sfd, 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,
> -	 * either cpufreq or counter driven. If the support status changes as
> -	 * a result of counter initialisation and use, retrigger the build of
> -	 * scheduling domains to ensure the information is propagated properly.
> -	 */
> -	if (!invariant)
> -		rebuild_sched_domains_energy();
>  }
>  
>  static int init_amu_fie_callback(struct notifier_block *nb, unsigned long val,
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 20b511949cd8..3631877f4440 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -23,6 +23,7 @@
>  
>  static DEFINE_PER_CPU(struct scale_freq_data *, sft_data);
>  static struct cpumask scale_freq_counters_mask;
> +static bool scale_freq_invariant;
>  
>  static bool supports_scale_freq_counters(const struct cpumask *cpus)
>  {
> @@ -35,6 +36,23 @@ bool topology_scale_freq_invariant(void)
>  	       supports_scale_freq_counters(cpu_online_mask);
>  }
>  
> +static void update_scale_freq_invariant(bool status)
> +{
> +	if (scale_freq_invariant == status)
> +		return;
> +
> +	/*
> +	 * Task scheduler behavior depends on frequency invariance support,
> +	 * either cpufreq or counter driven. If the support status changes as
> +	 * a result of counter initialisation and use, retrigger the build of
> +	 * scheduling domains to ensure the information is propagated properly.
> +	 */
> +	if (topology_scale_freq_invariant() == status) {
> +		scale_freq_invariant = status;
> +		rebuild_sched_domains_energy();
> +	}
> +}
> +
>  void topology_set_scale_freq_source(struct scale_freq_data *data,
>  				    const struct cpumask *cpus)
>  {
> @@ -50,6 +68,8 @@ void topology_set_scale_freq_source(struct scale_freq_data *data,
>  			cpumask_set_cpu(cpu, &scale_freq_counters_mask);
>  		}
>  	}

Small(ish) optimisation at the beginning of this function:

    if (cpumask_empty(&scale_freq_counters_mask))
        scale_freq_invariant = topology_scale_freq_invariant();

This will save you a call to rebuild_sched_domains_energy(), which is
quite expensive, when cpufreq supports FIE and we also have counters.

After comments addressed,

Reviewed-by: Ionela Voinescu <[email-masked]>
Tested-by: Ionela Voinescu <[email-masked]>

..for 1/2 and this addition.

Thanks,
Ionela.

> +
> +	update_scale_freq_invariant(true);
>  }
>  EXPORT_SYMBOL_GPL(topology_set_scale_freq_source);
>  
> @@ -67,6 +87,8 @@ void topology_clear_scale_freq_source(enum scale_freq_source source,
>  			cpumask_clear_cpu(cpu, &scale_freq_counters_mask);
>  		}
>  	}
> +
> +	update_scale_freq_invariant(false);
>  }
>  EXPORT_SYMBOL_GPL(topology_clear_scale_freq_source);
>  
> -- 
> 2.25.0.rc1.19.g042ed3e048af
> 
> -- 
> viresh

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