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Message-ID: <75bba88a-0516-a6a2-d4e6-8cedabadf413@arm.com>
Date: Wed, 30 Nov 2022 14:04:36 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
Sam Wu <wusamuel@...gle.com>,
Saravana Kannan <saravanak@...gle.com>,
Viresh Kumar <viresh.kumar@...aro.org>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
"Isaac J . Manjarres" <isaacmanjarres@...gle.com>,
kernel-team@...roid.com,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] Revert "cpufreq: schedutil: Move max CPU capacity to
sugov_policy"
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
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