[PATCH v2] psi: Remove the redundant psi_task_tick

[Chengming Zhou]

When the current task in a cgroup is in_memstall, the corresponding groupc
on that cpu is in PSI_MEM_FULL state, so we can exploit that to remove the
redundant psi_task_tick from scheduler_tick to save this periodic cost.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
---
 include/linux/psi.h  |  1 -
 kernel/sched/core.c  |  1 -
 kernel/sched/psi.c   | 49 ++++++++++++++-----------------------------------
 kernel/sched/stats.h |  9 ---------
 4 files changed, 14 insertions(+), 46 deletions(-)

diff --git a/include/linux/psi.h b/include/linux/psi.h
index 7361023f3fdd..65eb1476ac70 100644
--- a/include/linux/psi.h
+++ b/include/linux/psi.h
@@ -20,7 +20,6 @@ void psi_task_change(struct task_struct *task, int clear, int set);
 void psi_task_switch(struct task_struct *prev, struct task_struct *next,
 		     bool sleep);
 
-void psi_memstall_tick(struct task_struct *task, int cpu);
 void psi_memstall_enter(unsigned long *flags);
 void psi_memstall_leave(unsigned long *flags);
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 15d2562118d1..31788a9b335b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4533,7 +4533,6 @@ void scheduler_tick(void)
 	update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
 	curr->sched_class->task_tick(rq, curr, 0);
 	calc_global_load_tick(rq);
-	psi_task_tick(rq);
 
 	rq_unlock(rq, &rf);
 
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 2293c45d289d..6e46d9eb279b 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -644,8 +644,7 @@ static void poll_timer_fn(struct timer_list *t)
 	wake_up_interruptible(&group->poll_wait);
 }
 
-static void record_times(struct psi_group_cpu *groupc, int cpu,
-			 bool memstall_tick)
+static void record_times(struct psi_group_cpu *groupc, int cpu)
 {
 	u32 delta;
 	u64 now;
@@ -664,23 +663,6 @@ static void record_times(struct psi_group_cpu *groupc, int cpu,
 		groupc->times[PSI_MEM_SOME] += delta;
 		if (groupc->state_mask & (1 << PSI_MEM_FULL))
 			groupc->times[PSI_MEM_FULL] += delta;
-		else if (memstall_tick) {
-			u32 sample;
-			/*
-			 * Since we care about lost potential, a
-			 * memstall is FULL when there are no other
-			 * working tasks, but also when the CPU is
-			 * actively reclaiming and nothing productive
-			 * could run even if it were runnable.
-			 *
-			 * When the timer tick sees a reclaiming CPU,
-			 * regardless of runnable tasks, sample a FULL
-			 * tick (or less if it hasn't been a full tick
-			 * since the last state change).
-			 */
-			sample = min(delta, (u32)jiffies_to_nsecs(1));
-			groupc->times[PSI_MEM_FULL] += sample;
-		}
 	}
 
 	if (groupc->state_mask & (1 << PSI_CPU_SOME)) {
@@ -714,7 +696,7 @@ static void psi_group_change(struct psi_group *group, int cpu,
 	 */
 	write_seqcount_begin(&groupc->seq);
 
-	record_times(groupc, cpu, false);
+	record_times(groupc, cpu);
 
 	for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
 		if (!(m & (1 << t)))
@@ -738,6 +720,18 @@ static void psi_group_change(struct psi_group *group, int cpu,
 		if (test_state(groupc->tasks, s))
 			state_mask |= (1 << s);
 	}
+
+	/*
+	 * Since we care about lost potential, a memstall is FULL
+	 * when there are no other working tasks, but also when
+	 * the CPU is actively reclaiming and nothing productive
+	 * could run even if it were runnable. So when the current
+	 * task in a cgroup is in_memstall, the corresponding groupc
+	 * on that cpu is in PSI_MEM_FULL state.
+	 */
+	if (groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall)
+		state_mask |= (1 << PSI_MEM_FULL);
+
 	groupc->state_mask = state_mask;
 
 	write_seqcount_end(&groupc->seq);
@@ -859,21 +853,6 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
 	}
 }
 
-void psi_memstall_tick(struct task_struct *task, int cpu)
-{
-	struct psi_group *group;
-	void *iter = NULL;
-
-	while ((group = iterate_groups(task, &iter))) {
-		struct psi_group_cpu *groupc;
-
-		groupc = per_cpu_ptr(group->pcpu, cpu);
-		write_seqcount_begin(&groupc->seq);
-		record_times(groupc, cpu, true);
-		write_seqcount_end(&groupc->seq);
-	}
-}
-
 /**
  * psi_memstall_enter - mark the beginning of a memory stall section
  * @flags: flags to handle nested sections
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 33d0daf83842..9e4e67a94731 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -144,14 +144,6 @@ static inline void psi_sched_switch(struct task_struct *prev,
 	psi_task_switch(prev, next, sleep);
 }
 
-static inline void psi_task_tick(struct rq *rq)
-{
-	if (static_branch_likely(&psi_disabled))
-		return;
-
-	if (unlikely(rq->curr->in_memstall))
-		psi_memstall_tick(rq->curr, cpu_of(rq));
-}
 #else /* CONFIG_PSI */
 static inline void psi_enqueue(struct task_struct *p, bool wakeup) {}
 static inline void psi_dequeue(struct task_struct *p, bool sleep) {}
@@ -159,7 +151,6 @@ static inline void psi_ttwu_dequeue(struct task_struct *p) {}
 static inline void psi_sched_switch(struct task_struct *prev,
 				    struct task_struct *next,
 				    bool sleep) {}
-static inline void psi_task_tick(struct rq *rq) {}
 #endif /* CONFIG_PSI */
 
 #ifdef CONFIG_SCHED_INFO
-- 
2.11.0