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From:   Chengming Zhou <zhouchengming@bytedance.com>
To:     hannes@cmpxchg.org, surenb@google.com, mingo@redhat.com,
        peterz@infradead.org, tj@kernel.org, corbet@lwn.net,
        akpm@linux-foundation.org, rdunlap@infradead.org
Cc:     linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        songmuchun@bytedance.com, cgroups@vger.kernel.org,
        Chengming Zhou <zhouchengming@bytedance.com>
Subject: [PATCH 1/9] sched/psi: fix periodic aggregation shut off
Date:   Thu, 21 Jul 2022 12:04:31 +0800
Message-Id: <20220721040439.2651-2-zhouchengming@bytedance.com>
In-Reply-To: <20220721040439.2651-1-zhouchengming@bytedance.com>
References: <20220721040439.2651-1-zhouchengming@bytedance.com>
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We don't want to wake periodic aggregation work back up if the
task change is the aggregation worker itself going to sleep, or
we'll ping-pong forever.

Previously, we would use psi_task_change() in psi_dequeue() when
task going to sleep, so this check was put in psi_task_change().

But commit 4117cebf1a9f ("psi: Optimize task switch inside shared cgroups")
defer task sleep handling to psi_task_switch(), won't go through
psi_task_change() anymore.

So this patch move this check to psi_task_switch(). Note for defer sleep
case, we should wake periodic avgs work for common ancestors groups,
since those groups have next task sched_in.

Fixes: 4117cebf1a9f ("psi: Optimize task switch inside shared cgroups")
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 kernel/sched/psi.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index a337f3e35997..c8a4e644cd2c 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -800,7 +800,6 @@ void psi_task_change(struct task_struct *task, int clear, int set)
 {
 	int cpu = task_cpu(task);
 	struct psi_group *group;
-	bool wake_clock = true;
 	void *iter = NULL;
 	u64 now;
 
@@ -810,19 +809,9 @@ void psi_task_change(struct task_struct *task, int clear, int set)
 	psi_flags_change(task, clear, set);
 
 	now = cpu_clock(cpu);
-	/*
-	 * Periodic aggregation shuts off if there is a period of no
-	 * task changes, so we wake it back up if necessary. However,
-	 * don't do this if the task change is the aggregation worker
-	 * itself going to sleep, or we'll ping-pong forever.
-	 */
-	if (unlikely((clear & TSK_RUNNING) &&
-		     (task->flags & PF_WQ_WORKER) &&
-		     wq_worker_last_func(task) == psi_avgs_work))
-		wake_clock = false;
 
 	while ((group = iterate_groups(task, &iter)))
-		psi_group_change(group, cpu, clear, set, now, wake_clock);
+		psi_group_change(group, cpu, clear, set, now, true);
 }
 
 void psi_task_switch(struct task_struct *prev, struct task_struct *next,
@@ -858,6 +847,7 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
 
 	if (prev->pid) {
 		int clear = TSK_ONCPU, set = 0;
+		bool wake_clock = true;
 
 		/*
 		 * When we're going to sleep, psi_dequeue() lets us
@@ -871,13 +861,23 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
 				clear |= TSK_MEMSTALL_RUNNING;
 			if (prev->in_iowait)
 				set |= TSK_IOWAIT;
+
+			/*
+			 * Periodic aggregation shuts off if there is a period of no
+			 * task changes, so we wake it back up if necessary. However,
+			 * don't do this if the task change is the aggregation worker
+			 * itself going to sleep, or we'll ping-pong forever.
+			 */
+			if (unlikely((prev->flags & PF_WQ_WORKER) &&
+				     wq_worker_last_func(prev) == psi_avgs_work))
+				wake_clock = false;
 		}
 
 		psi_flags_change(prev, clear, set);
 
 		iter = NULL;
 		while ((group = iterate_groups(prev, &iter)) && group != common)
-			psi_group_change(group, cpu, clear, set, now, true);
+			psi_group_change(group, cpu, clear, set, now, wake_clock);
 
 		/*
 		 * TSK_ONCPU is handled up to the common ancestor. If we're tasked
-- 
2.36.1