Re: [PATCH v1] Revert "cpufreq: schedutil: Move max CPU capacity to sugov_policy"

[Vincent Guittot <vincent.guittot@linaro.org>]

On Wed, 30 Nov 2022 at 15:04, Lukasz Luba <lukasz.luba@arm.com> wrote:
>
> Hi Vincent,
>
> On 11/30/22 10:42, Vincent Guittot wrote:
> > Hi All
> >
> > Just for the log and because it took me a while to figure out the root
> > cause of the problem: This patch also creates a regression for
> > snapdragon845 based systems and probably on any QC chipsets that use a
> > LUT to update the OPP table at boot. The behavior is the same as
> > described by Sam with a staled value in sugov_policy.max field.
>
> Thanks for sharing this info and apologies that you spent cycles
> on it.
>
> I have checked that whole setup code (capacity + cpufreq policy and
> governor). It looks like to have a proper capacity of CPUs, we need
> to wait till the last policy is created. It's due to the arch_topology.c
> mechanism which is only triggered after all CPUs' got the policy.
> Unfortunately, this leads to a chicken & egg situation for this
> schedutil setup of max capacity.
>
> I have experimented with this code, which triggers an update in
> the schedutil, when all CPUs got the policy and sugov gov
> (with trace_printk() to mach the output below)

Your proposal below looks similar to what is done in arch_topology.c.
arch_topology.c triggers a rebuild of sched_domain and removes its
cpufreq notifier cb once it has visited all CPUs, could it also
trigger an update of CPU's policy with cpufreq_update_policy() ?

At this point you will be sure that the normalization has happened and
the max capacity will not change.

I don't know if it's a global problem or only for systems using arch_topology

>
> -------------------------8<-----------------------------------------
> diff --git a/kernel/sched/cpufreq_schedutil.c
> b/kernel/sched/cpufreq_schedutil.c
> index 9161d1136d01..f1913a857218 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -59,6 +59,7 @@ struct sugov_cpu {
>   };
>
>   static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu);
> +static cpumask_var_t cpus_to_visit;
>
>   /************************ Governor internals ***********************/
>
> @@ -783,6 +784,22 @@ static int sugov_start(struct cpufreq_policy *policy)
>
>                  cpufreq_add_update_util_hook(cpu, &sg_cpu->update_util,
> uu);
>          }
> +
> +       cpumask_andnot(cpus_to_visit, cpus_to_visit, policy->related_cpus);
> +
> +       if (cpumask_empty(cpus_to_visit)) {
> +               trace_printk("schedutil the visit cpu mask is empty now\n");
> +               for_each_possible_cpu(cpu) {
> +                       struct sugov_cpu *sg_cpu = &per_cpu(sugov_cpu, cpu);
> +                       struct sugov_policy *sg_policy = sg_cpu->sg_policy;
> +
> +                       sg_policy->max = arch_scale_cpu_capacity(cpu);
> +
> +                       trace_printk("SCHEDUTIL: NEW  CPU%u
> cpu_capacity=%lu\n",
> +                               cpu, sg_policy->max);
> +               }
> +       }
> +
>          return 0;
>   }
>
> @@ -800,6 +817,8 @@ static void sugov_stop(struct cpufreq_policy *policy)
>                  irq_work_sync(&sg_policy->irq_work);
>                  kthread_cancel_work_sync(&sg_policy->work);
>          }
> +
> +       cpumask_or(cpus_to_visit, cpus_to_visit, policy->related_cpus);
>   }
>
>   static void sugov_limits(struct cpufreq_policy *policy)
> @@ -829,6 +848,11 @@ struct cpufreq_governor schedutil_gov = {
>   #ifdef CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL
>   struct cpufreq_governor *cpufreq_default_governor(void)
>   {
> +       if (!alloc_cpumask_var(&cpus_to_visit, GFP_KERNEL))
> +               return NULL;
> +
> +       cpumask_copy(cpus_to_visit, cpu_possible_mask);
> +
>          return &schedutil_gov;
>   }
>   #endif
>
> ---------------------------------->8---------------------------------
>
>
> That simple approach fixes the issue. I have also tested it with
> governor change a few times and setting back the schedutil.
>
> -------------------------------------------
>     kworker/u12:1-48      [004] .....     2.208847: sugov_start:
> schedutil the visit cpu mask is empty now
>     kworker/u12:1-48      [004] .....     2.208854: sugov_start:
> SCHEDUTIL: NEW  CPU0 cpu_capacity=381
>     kworker/u12:1-48      [004] .....     2.208857: sugov_start:
> SCHEDUTIL: NEW  CPU1 cpu_capacity=381
>     kworker/u12:1-48      [004] .....     2.208860: sugov_start:
> SCHEDUTIL: NEW  CPU2 cpu_capacity=381
>     kworker/u12:1-48      [004] .....     2.208862: sugov_start:
> SCHEDUTIL: NEW  CPU3 cpu_capacity=381
>     kworker/u12:1-48      [004] .....     2.208864: sugov_start:
> SCHEDUTIL: NEW  CPU4 cpu_capacity=1024
>     kworker/u12:1-48      [004] .....     2.208866: sugov_start:
> SCHEDUTIL: NEW  CPU5 cpu_capacity=1024
>              bash-615     [005] .....    35.317113: sugov_start:
> schedutil the visit cpu mask is empty now
>              bash-615     [005] .....    35.317120: sugov_start:
> SCHEDUTIL: NEW  CPU0 cpu_capacity=381
>              bash-615     [005] .....    35.317123: sugov_start:
> SCHEDUTIL: NEW  CPU1 cpu_capacity=381
>              bash-615     [005] .....    35.317125: sugov_start:
> SCHEDUTIL: NEW  CPU2 cpu_capacity=381
>              bash-615     [005] .....    35.317127: sugov_start:
> SCHEDUTIL: NEW  CPU3 cpu_capacity=381
>              bash-615     [005] .....    35.317129: sugov_start:
> SCHEDUTIL: NEW  CPU4 cpu_capacity=1024
>              bash-615     [005] .....    35.317131: sugov_start:
> SCHEDUTIL: NEW  CPU5 cpu_capacity=1024
>              bash-623     [003] .....    57.633328: sugov_start:
> schedutil the visit cpu mask is empty now
>              bash-623     [003] .....    57.633336: sugov_start:
> SCHEDUTIL: NEW  CPU0 cpu_capacity=381
>              bash-623     [003] .....    57.633339: sugov_start:
> SCHEDUTIL: NEW  CPU1 cpu_capacity=381
>              bash-623     [003] .....    57.633340: sugov_start:
> SCHEDUTIL: NEW  CPU2 cpu_capacity=381
>              bash-623     [003] .....    57.633342: sugov_start:
> SCHEDUTIL: NEW  CPU3 cpu_capacity=381
>              bash-623     [003] .....    57.633343: sugov_start:
> SCHEDUTIL: NEW  CPU4 cpu_capacity=1024
>              bash-623     [003] .....    57.633344: sugov_start:
> SCHEDUTIL: NEW  CPU5 cpu_capacity=1024
> ----------------------------------------------------
>
> It should work.
>
> Regards,
> Lukasz