Re: [PATCH v4 7/7] arm64/amu: use capacity_ref_freq to set AMU ratio

Beata Michalska
2023-10-31T23:59:53Z

On Fri, Oct 27, 2023 at 10:04:00AM +0200, 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..626031076b75 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 assosciated 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 d4bef370feb3..3cba7dc753b3 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_ref_freq, cpu) * HZ_PER_KHZ);
> +
The capacity_ref_freq set earlier will still lead to units mismatch,
as at the point of calling topology_init_cpu_capacity_cppc the lowest & nominal
frequencies will be provided in MHz (unless I have missed smth).
This means that use of both, the capacity_ref_freq and the arch_freq_scale
will generate unexpected results, so I guess this should get amended in the
preceding patch (?) [1]

---
BR
B.

[1] https://lore.kernel.org/linux-arm-kernel/20231027080400.56703-4-vincent.guittot@linaro.org/T/#m42daa167097edc190b1cfc05382c385ed801d909

> 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_ref_freq, cpu) = policy->cpuinfo.max_freq;
> + freq_inv_set_max_ratio(cpu,
> + per_cpu(capacity_ref_freq, 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 38ca6c76af56..ffdf0b7c55fa 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
>