Re: [PATCH 3/3] ACPI: cpufreq: Add ITMT support when CPPC enabled for Zhaoxin CPUs

[Ricardo Neri]

On Thu, Dec 28, 2023 at 03:57:05PM +0800, Tony W Wang-oc wrote:
> For Zhaoxin CPUs, the cores' highest frequencies may be different, which
> means that cores may run at different max frequencies,
> 
> According to ACPI-spec6 chapter 8.4.7, the per-core highest frequency
> value can be obtained via cppc.
> 
> The core with the higher frequency have better performance, which can be
> called as preferred core. And better performance can be achieved by
> making the scheduler to run tasks on these preferred cores.
> 
> The cpufreq driver can use the highest frequency value as the prioriy of
> core to make the scheduler try to get better performace. More specifically,
> in the acpi-cpufreq driver use cppc_get_highest_perf() to get highest
> frequency value of each core, use sched_set_itmt_core_prio() to set
> highest frequency value as core priority, and use sched_set_itmt_support()
> provided by ITMT to tell the scheduler to favor on the preferred cores.
> 
> Signed-off-by: Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx>
> ---
>  drivers/cpufreq/acpi-cpufreq.c | 56 +++++++++++++++++++++++++++++++++-
>  1 file changed, 55 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> index 37f1cdf46d29..f4c1ff9e4bb0 100644
> --- a/drivers/cpufreq/acpi-cpufreq.c
> +++ b/drivers/cpufreq/acpi-cpufreq.c
> @@ -663,8 +663,56 @@ static u64 get_max_boost_ratio(unsigned int cpu)
>  
>  	return div_u64(highest_perf << SCHED_CAPACITY_SHIFT, nominal_perf);
>  }
> +
> +/* The work item is needed to avoid CPU hotplug locking issues */
> +static void sched_itmt_work_fn(struct work_struct *work)
> +{
> +	sched_set_itmt_support();
> +}
> +
> +static DECLARE_WORK(sched_itmt_work, sched_itmt_work_fn);
> +
> +static void set_itmt_prio(int cpu)
> +{
> +	static bool cppc_highest_perf_diff;
> +	static struct cpumask core_prior_mask;
> +	u64 highest_perf;
> +	static u64 max_highest_perf = 0, min_highest_perf = U64_MAX;
> +	int ret;
> +
> +	ret = cppc_get_highest_perf(cpu, &highest_perf);
> +	if (ret)
> +		return;
> +
> +	sched_set_itmt_core_prio(highest_perf, cpu);
> +	cpumask_set_cpu(cpu, &core_prior_mask);
> +
> +	if (max_highest_perf <= min_highest_perf) {
> +		if (highest_perf > max_highest_perf)
> +			max_highest_perf = highest_perf;
> +
> +		if (highest_perf < min_highest_perf)
> +			min_highest_perf = highest_perf;
> +
> +		if (max_highest_perf > min_highest_perf) {
> +			/*
> +			 * This code can be run during CPU online under the
> +			 * CPU hotplug locks, so sched_set_itmt_support()
> +			 * cannot be called from here.  Queue up a work item
> +			 * to invoke it.
> +			 */
> +			cppc_highest_perf_diff = true;
> +		}
> +	}
> +
> +	if (cppc_highest_perf_diff && cpumask_equal(&core_prior_mask, cpu_online_mask)) {
> +		pr_debug("queue a work to set itmt enabled\n");
> +		schedule_work(&sched_itmt_work);
> +	}
> +}

sched_itmt_work and this function is a duplicate of what the intel_pstate
driver already does. It might be good if consolidate in a single place
if you are going to pursue this approach.