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>
---
 arch/arm64/kernel/topology.c  | 26 ++++++++++++++------------
 drivers/base/arch_topology.c  | 12 +++++++++++-
 include/linux/arch_topology.h |  1 +
 3 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 817d788cd866..615c1a20129f 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 +144,12 @@ 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;
+	WRITE_ONCE(per_cpu(arch_max_freq_scale, cpu), (unsigned long)ratio);
 
-	return 0;
+	return;
 }
 
 static void amu_scale_freq_tick(void)
@@ -195,10 +200,7 @@ 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);
+	}
 
 	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

On Sat, Nov 04, 2023 at 11:59:07AM +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>
> ---
>  arch/arm64/kernel/topology.c  | 26 ++++++++++++++------------
>  drivers/base/arch_topology.c  | 12 +++++++++++-
>  include/linux/arch_topology.h |  1 +
>  3 files changed, 26 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 817d788cd866..615c1a20129f 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);

This doesn't seem to match the comment? SCHED_CAPACITY_SCALE doesn't have
the '2 *' multiplier.

>  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 +144,12 @@ 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;
> +	WRITE_ONCE(per_cpu(arch_max_freq_scale, cpu), (unsigned long)ratio);

Why is WRITE_ONCE() now needed?

> -	return 0;
> +	return;

Pointless 'return;' statement.

Will

On Tue, 7 Nov 2023 at 11:38, Will Deacon <will@kernel.org> wrote:
>
> On Sat, Nov 04, 2023 at 11:59:07AM +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>
> > ---
> >  arch/arm64/kernel/topology.c  | 26 ++++++++++++++------------
> >  drivers/base/arch_topology.c  | 12 +++++++++++-
> >  include/linux/arch_topology.h |  1 +
> >  3 files changed, 26 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> > index 817d788cd866..615c1a20129f 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);
>
> This doesn't seem to match the comment? SCHED_CAPACITY_SCALE doesn't have
> the '2 *' multiplier.

The comment in freq_inv_set_max_ratio() says:

* We use a factor of 2 * SCHED_CAPACITY_SHIFT -> SCHED_CAPACITY_SCALE²
* in order to ensure a good resolution for arch_max_freq_scale for
* very low reference frequencies (down to the KHz range which should
* be unlikely).

Then there is a  "  * arch_max_freq_scale) >> SCHED_CAPACITY_SHIFT"
when computing the scale which brings the result back to
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 +144,12 @@ 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;
> > +     WRITE_ONCE(per_cpu(arch_max_freq_scale, cpu), (unsigned long)ratio);
>
> Why is WRITE_ONCE() now needed?

the tick can already use it. We want to make sure to use either the
old or the new one but not an intermediate value

>
> > -     return 0;
> > +     return;
>
> Pointless 'return;' statement.

fair enough

>
> Will

On Tue, Nov 07, 2023 at 12:18:20PM +0100, Vincent Guittot wrote:
> On Tue, 7 Nov 2023 at 11:38, Will Deacon <will@kernel.org> wrote:
> >
> > On Sat, Nov 04, 2023 at 11:59:07AM +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>
> > > ---
> > >  arch/arm64/kernel/topology.c  | 26 ++++++++++++++------------
> > >  drivers/base/arch_topology.c  | 12 +++++++++++-
> > >  include/linux/arch_topology.h |  1 +
> > >  3 files changed, 26 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> > > index 817d788cd866..615c1a20129f 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);
> >
> > This doesn't seem to match the comment? SCHED_CAPACITY_SCALE doesn't have
> > the '2 *' multiplier.
> 
> The comment in freq_inv_set_max_ratio() says:
> 
> * We use a factor of 2 * SCHED_CAPACITY_SHIFT -> SCHED_CAPACITY_SCALE²
> * in order to ensure a good resolution for arch_max_freq_scale for
> * very low reference frequencies (down to the KHz range which should
> * be unlikely).
> 
> Then there is a  "  * arch_max_freq_scale) >> SCHED_CAPACITY_SHIFT"
> when computing the scale which brings the result back to
> SCHED_CAPACITY_SHIFT

Ah, I see; I'd not spotted that amu_scale_freq_tick() is doing some
arithmetic on the value (it doesn't return anything because it's 'void').
It's slightly confusing because the comment talks about SCHED_CAPACITY_SCALE
whereas all the code works on the shift, but I get it now.

> > >  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 +144,12 @@ 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;
> > > +     WRITE_ONCE(per_cpu(arch_max_freq_scale, cpu), (unsigned long)ratio);
> >
> > Why is WRITE_ONCE() now needed?
> 
> the tick can already use it. We want to make sure to use either the
> old or the new one but not an intermediate value

Isn't that already the case without this patch? In other words, this should
be a separate change.

Will

On Tue, 7 Nov 2023 at 13:01, Will Deacon <will@kernel.org> wrote:
>
> On Tue, Nov 07, 2023 at 12:18:20PM +0100, Vincent Guittot wrote:
> > On Tue, 7 Nov 2023 at 11:38, Will Deacon <will@kernel.org> wrote:
> > >
> > > On Sat, Nov 04, 2023 at 11:59:07AM +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>
> > > > ---
> > > >  arch/arm64/kernel/topology.c  | 26 ++++++++++++++------------
> > > >  drivers/base/arch_topology.c  | 12 +++++++++++-
> > > >  include/linux/arch_topology.h |  1 +
> > > >  3 files changed, 26 insertions(+), 13 deletions(-)
> > > >
> > > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> > > > index 817d788cd866..615c1a20129f 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);
> > >
> > > This doesn't seem to match the comment? SCHED_CAPACITY_SCALE doesn't have
> > > the '2 *' multiplier.
> >
> > The comment in freq_inv_set_max_ratio() says:
> >
> > * We use a factor of 2 * SCHED_CAPACITY_SHIFT -> SCHED_CAPACITY_SCALE²
> > * in order to ensure a good resolution for arch_max_freq_scale for
> > * very low reference frequencies (down to the KHz range which should
> > * be unlikely).
> >
> > Then there is a  "  * arch_max_freq_scale) >> SCHED_CAPACITY_SHIFT"
> > when computing the scale which brings the result back to
> > SCHED_CAPACITY_SHIFT
>
> Ah, I see; I'd not spotted that amu_scale_freq_tick() is doing some
> arithmetic on the value (it doesn't return anything because it's 'void').
> It's slightly confusing because the comment talks about SCHED_CAPACITY_SCALE
> whereas all the code works on the shift, but I get it now.
>
> > > >  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 +144,12 @@ 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;
> > > > +     WRITE_ONCE(per_cpu(arch_max_freq_scale, cpu), (unsigned long)ratio);
> > >
> > > Why is WRITE_ONCE() now needed?
> >
> > the tick can already use it. We want to make sure to use either the
> > old or the new one but not an intermediate value
>
> Isn't that already the case without this patch? In other words, this should
> be a separate change.

Currently the ratio is set in the same notifier callback before
registering the AMU function in topology_scale_freq_tick whereas there
are now done in 2 separate notifier callbacks (still for the same
event) but we don't know the order

>
> Will