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

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Date:   Tue, 20 Oct 2020 17:44:40 +0200
From:   Redha Gouicem <redha.gouicem@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     julien.sopena@...6.fr, julia.lawall@...ia.fr,
        gilles.muller@...ia.fr, carverdamien@...il.com,
        jean-pierre.lozi@...cle.com, baptiste.lepers@...ney.edu.au,
        nicolas.palix@...v-grenoble-alpes.fr,
        willy.zwaenepoel@...ney.edu.au,
        Redha Gouicem <redha.gouicem@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        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>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Qais Yousef <qais.yousef@....com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Guilherme G. Piccoli" <gpiccoli@...onical.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: [PATCH 2/3] sched: core: x86: query frequency at each tick

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@...il.com>
Signed-off-by: Damien Carver <carverdamien@...il.com>
Signed-off-by: Redha Gouicem <redha.gouicem@...il.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