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

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Date:   Thu, 2 Nov 2023 10:06:50 +0100
From:   Pierre Gondois <pierre.gondois@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        linux@...linux.org.uk, catalin.marinas@....com, will@...nel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, sudeep.holla@....com,
        gregkh@...uxfoundation.org, rafael@...nel.org, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        viresh.kumar@...aro.org, lenb@...nel.org, robert.moore@...el.com,
        lukasz.luba@....com, ionela.voinescu@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-pm@...r.kernel.org,
        linux-acpi@...r.kernel.org, acpica-devel@...ts.linuxfoundation.org
Cc:     conor.dooley@...rochip.com, suagrfillet@...il.com,
        ajones@...tanamicro.com, lftan@...nel.org
Subject: Re: [PATCH v4 6/7] cpufreq/cppc: set the frequency used for computing
 the capacity

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@...aro.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");
>