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

[Lukasz Luba <lukasz.luba@arm.com>]

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)

-------------------------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