Re: [PATCH v6 7/7] arm64/amu: Use capacity_ref_freq to set AMU ratio

[Beata Michalska <beata.michalska@arm.com>]

On Tue, Nov 14, 2023 at 02:07:01PM +0100, Beata Michalska wrote:
> On Thu, Nov 09, 2023 at 11:14:38AM +0100, Vincent Guittot wrote:
> > Use the new capacity_ref_freq to set the ratio that is used by AMU for
> > computing the arch_scale_freq_capacity().
> > This helps to keep everything aligned using the same reference for
> > computing CPUs capacity.
> > 
> > The default value of the ratio (stored in per_cpu(arch_max_freq_scale))
> > ensures that arch_scale_freq_capacity() returns max capacity until it is
> > set to its correct value with the cpu capacity and capacity_ref_freq.
> > 
> > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> > Acked-by: Sudeep Holla <sudeep.holla@arm.com>
> > ---
> >  arch/arm64/kernel/topology.c  | 26 +++++++++++++-------------
> >  drivers/base/arch_topology.c  | 12 +++++++++++-
> >  include/linux/arch_topology.h |  1 +
> >  3 files changed, 25 insertions(+), 14 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> > index 817d788cd866..1a2c72f3e7f8 100644
> > --- a/arch/arm64/kernel/topology.c
> > +++ b/arch/arm64/kernel/topology.c
> > @@ -82,7 +82,12 @@ int __init parse_acpi_topology(void)
> >  #undef pr_fmt
> >  #define pr_fmt(fmt) "AMU: " fmt
> >  
> > -static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale);
> > +/*
> > + * Ensure that amu_scale_freq_tick() will return SCHED_CAPACITY_SCALE until
> > + * the CPU capacity and its associated frequency have been correctly
> > + * initialized.
> > + */
> > +static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale) =  1UL << (2 * SCHED_CAPACITY_SHIFT);
> >  static DEFINE_PER_CPU(u64, arch_const_cycles_prev);
> >  static DEFINE_PER_CPU(u64, arch_core_cycles_prev);
> >  static cpumask_var_t amu_fie_cpus;
> > @@ -112,14 +117,14 @@ static inline bool freq_counters_valid(int cpu)
> >  	return true;
> >  }
> >  
> > -static int freq_inv_set_max_ratio(int cpu, u64 max_rate, u64 ref_rate)
> > +void freq_inv_set_max_ratio(int cpu, u64 max_rate)
> >  {
> > -	u64 ratio;
> > +	u64 ratio, ref_rate = arch_timer_get_rate();
> >  
> >  	if (unlikely(!max_rate || !ref_rate)) {
> > -		pr_debug("CPU%d: invalid maximum or reference frequency.\n",
> > +		WARN_ONCE(1, "CPU%d: invalid maximum or reference frequency.\n",
> >  			 cpu);
> > -		return -EINVAL;
> > +		return;
> >  	}
> >  
> >  	/*
> > @@ -139,12 +144,10 @@ static int freq_inv_set_max_ratio(int cpu, u64 max_rate, u64 ref_rate)
> >  	ratio = div64_u64(ratio, max_rate);
> >  	if (!ratio) {
> >  		WARN_ONCE(1, "Reference frequency too low.\n");
> > -		return -EINVAL;
> > +		return;
> >  	}
> >  
> > -	per_cpu(arch_max_freq_scale, cpu) = (unsigned long)ratio;
> > -
> > -	return 0;
> > +	WRITE_ONCE(per_cpu(arch_max_freq_scale, cpu), (unsigned long)ratio);
> >  }
> >  
> >  static void amu_scale_freq_tick(void)
> > @@ -195,10 +198,7 @@ static void amu_fie_setup(const struct cpumask *cpus)
> >  		return;
> >  
> >  	for_each_cpu(cpu, cpus) {
> > -		if (!freq_counters_valid(cpu) ||
> > -		    freq_inv_set_max_ratio(cpu,
> > -					   cpufreq_get_hw_max_freq(cpu) * 1000ULL,
> > -					   arch_timer_get_rate()))
> > +		if (!freq_counters_valid(cpu))
> 
> >  			return;
> >  	}
> >  
> > diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> > index 0a2e43728286..0906114963ff 100644
> > --- a/drivers/base/arch_topology.c
> > +++ b/drivers/base/arch_topology.c
> > @@ -344,6 +344,10 @@ bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)
> >  	return !ret;
> >  }
> >  
> > +void __weak freq_inv_set_max_ratio(int cpu, u64 max_rate)
> > +{
> > +}
> > +
> >  #ifdef CONFIG_ACPI_CPPC_LIB
> >  #include <acpi/cppc_acpi.h>
> >  
> > @@ -381,6 +385,9 @@ void topology_init_cpu_capacity_cppc(void)
> >  	}
> >  
> >  	for_each_possible_cpu(cpu) {
> > +		freq_inv_set_max_ratio(cpu,
> > +				       per_cpu(capacity_freq_ref, cpu) * HZ_PER_KHZ);
> > +
> >  		capacity = raw_capacity[cpu];
> >  		capacity = div64_u64(capacity << SCHED_CAPACITY_SHIFT,
> >  				     capacity_scale);
> > @@ -422,8 +429,11 @@ init_cpu_capacity_callback(struct notifier_block *nb,
> >  
> >  	cpumask_andnot(cpus_to_visit, cpus_to_visit, policy->related_cpus);
> >  
> > -	for_each_cpu(cpu, policy->related_cpus)
> > +	for_each_cpu(cpu, policy->related_cpus) {
> >  		per_cpu(capacity_freq_ref, cpu) = policy->cpuinfo.max_freq;
> > +		freq_inv_set_max_ratio(cpu,
> > +				       per_cpu(capacity_freq_ref, cpu) * HZ_PER_KHZ);
> > +	}
> Just wondering if this is really necessary as freq_inv_set_max_ratio will
> originally be called upon cpufreq notification being triggered (with
> CPUFREQ_CREATE_POLICY event) which should happen after the newly introduced
> capacity_freq_ref gets properly set up, so wouldn't the change of flipping
> cpufreq_get_hw_max_freq(cpu) to capacity_freq_ref do just fine ?
> Then pushing AMU specific call to generic arch code  would not be necessary.
> Or did I miss smth on the way ?
> 
I guess you can ignore my comment as init_cpu_capacity_callback (where we now
set the capacity_freq_ref) works on the same basis so there is no guarantee it
will be triggered before AMU callback.
Still having the freq_inv_set_max_ratio sitting in arch_topology.c somehow
doesn't sit well with me. We could potentially check capacity_freq_ref against
its init value and act accordingly but that is gruesome as well.

> ---
> BR
> B.
> 
> >  
> >  	if (cpumask_empty(cpus_to_visit)) {
> >  		topology_normalize_cpu_scale();
> > diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
> > index 32c24ff4f2a8..a63d61ca55af 100644
> > --- a/include/linux/arch_topology.h
> > +++ b/include/linux/arch_topology.h
> > @@ -99,6 +99,7 @@ void update_siblings_masks(unsigned int cpu);
> >  void remove_cpu_topology(unsigned int cpuid);
> >  void reset_cpu_topology(void);
> >  int parse_acpi_topology(void);
> > +void freq_inv_set_max_ratio(int cpu, u64 max_rate);
> >  #endif
> >  
> >  #endif /* _LINUX_ARCH_TOPOLOGY_H_ */
> > -- 
> > 2.34.1
> >