[PATCH 2/3] sched: core: x86: query frequency at each tick

[Redha Gouicem <redha.gouicem@gmail.com>]

Query the current frequency of the core during the scheduler tick.
The scheduler subsystem maintains its own copies of the aperf/mperf
structure because it will query the frequency more frequently than what
the cpufreq subsystem does. This can lead to inaccurate measurements,
but it is not problematic here.

Co-developed-by: Damien Carver <carverdamien@gmail.com>
Signed-off-by: Damien Carver <carverdamien@gmail.com>
Signed-off-by: Redha Gouicem <redha.gouicem@gmail.com>
---
 kernel/sched/core.c  | 11 +++++++++++
 kernel/sched/sched.h |  4 ++++
 2 files changed, 15 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c36dc1ae58be..d6d27a6fc23c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3976,6 +3976,15 @@ unsigned long long task_sched_runtime(struct task_struct *p)
 	return ns;
 }
 
+struct freq_sample {
+	unsigned int  khz;
+	ktime_t       time;
+	u64           aperf;
+	u64           mperf;
+};
+
+DEFINE_PER_CPU(struct freq_sample, freq_sample);
+
 /*
  * This function gets called by the timer code, with HZ frequency.
  * We call it with interrupts disabled.
@@ -3996,6 +4005,8 @@ void scheduler_tick(void)
 	update_rq_clock(rq);
 	thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
 	update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
+	rq->freq = arch_freq_get_on_cpu_from_sample(cpu,
+						    this_cpu_ptr(&freq_sample));
 	curr->sched_class->task_tick(rq, curr, 0);
 	calc_global_load_tick(rq);
 	psi_task_tick(rq);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 28709f6b0975..7d794ab756d2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1048,6 +1048,10 @@ struct rq {
 	/* Must be inspected within a rcu lock section */
 	struct cpuidle_state	*idle_state;
 #endif
+
+	/* Frequency measured at the last tick */
+	unsigned int            freq;
+
 };
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-- 
2.28.0