Re: [PATCH v4 6/7] cpufreq/cppc: set the frequency used for computing the capacity

Pierre Gondois
2023-11-02T09:07:02Z

Hello Vincent,

On 10/27/23 10:03, Vincent Guittot wrote:
> Save the frequency associated to the performance that has been used when
> initializing the capacity of CPUs.
> Also, cppc cpufreq driver can register an artificial energy model. In such
> case, it needs the frequency for this compute capacity.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> drivers/base/arch_topology.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 9a073c2d2086..d4bef370feb3 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -349,6 +349,7 @@ bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)
>
> void topology_init_cpu_capacity_cppc(void)
> {
> + u64 capacity, capacity_scale = 0;
> struct cppc_perf_caps perf_caps;
> int cpu;
>
> @@ -365,6 +366,10 @@ void topology_init_cpu_capacity_cppc(void)
> (perf_caps.highest_perf >= perf_caps.nominal_perf) &&
> (perf_caps.highest_perf >= perf_caps.lowest_perf)) {
> raw_capacity[cpu] = perf_caps.highest_perf;
> + capacity_scale = max_t(u64, capacity_scale, raw_capacity[cpu]);
> +
> + per_cpu(capacity_ref_freq, cpu) = cppc_perf_to_khz(&perf_caps, raw_capacity[cpu]);
> +

To continue Beata's point, I think there is an issue with the following:
cppc_perf_to_khz() and cppc_khz_to_perf() were previously used with a struct containing
frequencies in KHz, cf. [1].
In the original _CPC object, frequencies are in MHz. It means that the perf_caps struct
here contains frequencies in MHz, and per_cpu(capacity_ref_freq, cpu) is in MHz aswell.

[1] https://github.com/torvalds/linux/blob/master/drivers/cpufreq/cppc_cpufreq.c#L682

> pr_debug("cpu_capacity: CPU%d cpu_capacity=%u (raw).\n",
> cpu, raw_capacity[cpu]);
> continue;
> @@ -375,7 +380,15 @@ void topology_init_cpu_capacity_cppc(void)
> goto exit;
> }
>
> - topology_normalize_cpu_scale();
> + for_each_possible_cpu(cpu) {
> + capacity = raw_capacity[cpu];
> + capacity = div64_u64(capacity << SCHED_CAPACITY_SHIFT,
> + capacity_scale);
> + topology_set_cpu_scale(cpu, capacity);
> + pr_debug("cpu_capacity: CPU%d cpu_capacity=%lu\n",
> + cpu, topology_get_cpu_scale(cpu));
> + }
> +
> schedule_work(&update_topology_flags_work);
> pr_debug("cpu_capacity: cpu_capacity initialization done\n");
>