psi: track changed states

Introduce changed_states parameter into collect_percpu_times to track
the states changed since the last update.

This will be needed to detect whether polled states activated in the
monitor patch.

Link: http://lkml.kernel.org/r/20190319235619.260832-6-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

@@ -210,14 +210,17 @@ static bool test_state(unsigned int *tasks, enum psi_states state)
 	}
 }
 
-static void get_recent_times(struct psi_group *group, int cpu, u32 *times)
+static void get_recent_times(struct psi_group *group, int cpu, u32 *times,
+			     u32 *pchanged_states)
 {
 	struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
 	u64 now, state_start;
 	enum psi_states s;
 	unsigned int seq;
 	u32 state_mask;
 
+	*pchanged_states = 0;
+
 	/* Snapshot a coherent view of the CPU state */
 	do {
 		seq = read_seqcount_begin(&groupc->seq);
@@ -246,6 +249,8 @@ static void get_recent_times(struct psi_group *group, int cpu, u32 *times)
 		groupc->times_prev[s] = times[s];
 
 		times[s] = delta;
+		if (delta)
+			*pchanged_states |= (1 << s);
 	}
 }
 
@@ -269,10 +274,11 @@ static void calc_avgs(unsigned long avg[3], int missed_periods,
 	avg[2] = calc_load(avg[2], EXP_300s, pct);
 }
 
-static bool collect_percpu_times(struct psi_group *group)
+static void collect_percpu_times(struct psi_group *group, u32 *pchanged_states)
 {
 	u64 deltas[NR_PSI_STATES - 1] = { 0, };
 	unsigned long nonidle_total = 0;
+	u32 changed_states = 0;
 	int cpu;
 	int s;
 
@@ -287,8 +293,11 @@ static bool collect_percpu_times(struct psi_group *group)
 	for_each_possible_cpu(cpu) {
 		u32 times[NR_PSI_STATES];
 		u32 nonidle;
+		u32 cpu_changed_states;
 
-		get_recent_times(group, cpu, times);
+		get_recent_times(group, cpu, times,
+				&cpu_changed_states);
+		changed_states |= cpu_changed_states;
 
 		nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]);
 		nonidle_total += nonidle;
@@ -313,7 +322,8 @@ static bool collect_percpu_times(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;
+	if (pchanged_states)
+		*pchanged_states = changed_states;
 }
 
 static u64 update_averages(struct psi_group *group, u64 now)
@@ -373,6 +383,7 @@ static void psi_avgs_work(struct work_struct *work)
 {
 	struct delayed_work *dwork;
 	struct psi_group *group;
+	u32 changed_states;
 	bool nonidle;
 	u64 now;
 
@@ -383,7 +394,8 @@ static void psi_avgs_work(struct work_struct *work)
 
 	now = sched_clock();
 
-	nonidle = collect_percpu_times(group);
+	collect_percpu_times(group, &changed_states);
+	nonidle = changed_states & (1 << PSI_NONIDLE);
 	/*
 	 * If there is task activity, periodically fold the per-cpu
 	 * times and feed samples into the running averages. If things
@@ -719,7 +731,7 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
 	/* Update averages before reporting them */
 	mutex_lock(&group->avgs_lock);
 	now = sched_clock();
-	collect_percpu_times(group);
+	collect_percpu_times(group, NULL);
 	if (now >= group->avg_next_update)
 		group->avg_next_update = update_averages(group, now);
 	mutex_unlock(&group->avgs_lock);