psi: split update_stats into parts

Split update_stats into collect_percpu_times and update_averages for
collect_percpu_times to be reused later inside psi monitor.

Link: http://lkml.kernel.org/r/20190319235619.260832-5-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sched/psi.c

@@ -269,17 +269,13 @@ static void calc_avgs(unsigned long avg[3], int missed_periods,
 	avg[2] = calc_load(avg[2], EXP_300s, pct);
 }
 
-static bool update_stats(struct psi_group *group)
+static bool collect_percpu_times(struct psi_group *group)
 {
 	u64 deltas[NR_PSI_STATES - 1] = { 0, };
-	unsigned long missed_periods = 0;
 	unsigned long nonidle_total = 0;
-	u64 now, expires, period;
 	int cpu;
 	int s;
 
-	mutex_lock(&group->avgs_lock);
-
 	/*
 	 * Collect the per-cpu time buckets and average them into a
 	 * single time sample that is normalized to wallclock time.
@@ -317,11 +313,18 @@ static bool update_stats(struct psi_group *group)
 	for (s = 0; s < NR_PSI_STATES - 1; s++)
 		group->total[s] += div_u64(deltas[s], max(nonidle_total, 1UL));
 
+	return nonidle_total;
+}
+
+static u64 update_averages(struct psi_group *group, u64 now)
+{
+	unsigned long missed_periods = 0;
+	u64 expires, period;
+	u64 avg_next_update;
+	int s;
+
 	/* avgX= */
-	now = sched_clock();
 	expires = group->avg_next_update;
-	if (now < expires)
-		goto out;
 	if (now - expires >= psi_period)
 		missed_periods = div_u64(now - expires, psi_period);
 
@@ -332,7 +335,7 @@ static bool update_stats(struct psi_group *group)
 	 * But the deltas we sample out of the per-cpu buckets above
 	 * are based on the actual time elapsing between clock ticks.
 	 */
-	group->avg_next_update = expires + ((1 + missed_periods) * psi_period);
+	avg_next_update = expires + ((1 + missed_periods) * psi_period);
 	period = now - (group->avg_last_update + (missed_periods * psi_period));
 	group->avg_last_update = now;
 
@@ -362,40 +365,41 @@ static bool update_stats(struct psi_group *group)
 		group->avg_total[s] += sample;
 		calc_avgs(group->avg[s], missed_periods, sample, period);
 	}
-out:
-	mutex_unlock(&group->avgs_lock);
-	return nonidle_total;
+
+	return avg_next_update;
 }
 
 static void psi_avgs_work(struct work_struct *work)
 {
 	struct delayed_work *dwork;
 	struct psi_group *group;
 	bool nonidle;
+	u64 now;
 
 	dwork = to_delayed_work(work);
 	group = container_of(dwork, struct psi_group, avgs_work);
 
+	mutex_lock(&group->avgs_lock);
+
+	now = sched_clock();
+
+	nonidle = collect_percpu_times(group);
 	/*
 	 * If there is task activity, periodically fold the per-cpu
 	 * times and feed samples into the running averages. If things
 	 * are idle and there is no data to process, stop the clock.
 	 * Once restarted, we'll catch up the running averages in one
 	 * go - see calc_avgs() and missed_periods.
 	 */
-
-	nonidle = update_stats(group);
+	if (now >= group->avg_next_update)
+		group->avg_next_update = update_averages(group, now);
 
 	if (nonidle) {
-		unsigned long delay = 0;
-		u64 now;
-
-		now = sched_clock();
-		if (group->avg_next_update > now)
-			delay = nsecs_to_jiffies(
-					group->avg_next_update - now) + 1;
-		schedule_delayed_work(dwork, delay);
+		schedule_delayed_work(dwork, nsecs_to_jiffies(
+				group->avg_next_update - now) + 1);
 	}
+
+	mutex_unlock(&group->avgs_lock);
 }
 
 static void record_times(struct psi_group_cpu *groupc, int cpu,
@@ -707,11 +711,18 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
 int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
 {
 	int full;
+	u64 now;
 
 	if (static_branch_likely(&psi_disabled))
 		return -EOPNOTSUPP;
 
-	update_stats(group);
+	/* Update averages before reporting them */
+	mutex_lock(&group->avgs_lock);
+	now = sched_clock();
+	collect_percpu_times(group);
+	if (now >= group->avg_next_update)
+		group->avg_next_update = update_averages(group, now);
+	mutex_unlock(&group->avgs_lock);
 
 	for (full = 0; full < 2 - (res == PSI_CPU); full++) {
 		unsigned long avg[3];