linux-kernel - [PATCH] sched/debug: Show intergroup and hierarchy sum wait time of a task group

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Date:   Wed, 23 Jan 2019 17:46:56 +0800
From:   ufo19890607@...il.com
To:     mingo@...hat.com, peterz@...radead.org, yun.wang@...ux.alibaba.com,
        yuzhoujian@...ichuxing.com
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] sched/debug: Show intergroup and hierarchy sum wait time of a task group

From: yuzhoujian <yuzhoujian@...ichuxing.com>

We can monitor the sum wait time of a task group since 'commit 3d6c50c27bd6
("sched/debug: Show the sum wait time of a task group")'. However this
wait_sum just represents the confilct between different task groups, since
it is simply sum the wait time of task_group's cfs_rq. And we still cannot
evaluate the conflict between all the tasks within hierarchy of this group,
so the hierarchy wait time is still needed.

Thus we introduce hierarchy wait_sum which summarizes the total wait sum of
all the tasks in the hierarchy of a group.

The 'cpu.stat' is modified to show the statistic, like:

	nr_periods 0
	nr_throttled 0
	throttled_time 0
	intergroup wait_sum 2842251984
	hierarchy wait_sum 6389509389332798

>From now on we can monitor both the wait_sum of intergroup and hierarchy,
which will inevitably help a system administrator know how intense the CPU
competition is within a task group and between different task groups. We
can calculate the wait rate of a task group based on hierarchy wait_sum and
cpuacct.usage.

For example:
	X% = (current_wait_sum - last_wait_sum) / ((current_usage -
last_usage) + (current_wait_sum - last_wait_sum))

That means the task group paid X percentage of time on runqueue waiting
for the CPU.

Signed-off-by: yuzhoujian <yuzhoujian@...ichuxing.com>
---
 kernel/sched/core.c  | 11 +++++++----
 kernel/sched/fair.c  | 17 +++++++++++++++++
 kernel/sched/sched.h |  3 +++
 3 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ee77636..172e6fb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6760,13 +6760,16 @@ static int cpu_cfs_stat_show(struct seq_file *sf, void *v)
 	seq_printf(sf, "throttled_time %llu\n", cfs_b->throttled_time);
 
 	if (schedstat_enabled() && tg != &root_task_group) {
-		u64 ws = 0;
+		u64 inter_ws = 0, hierarchy_ws = 0;
 		int i;
 
-		for_each_possible_cpu(i)
-			ws += schedstat_val(tg->se[i]->statistics.wait_sum);
+		for_each_possible_cpu(i) {
+			inter_ws += schedstat_val(tg->se[i]->statistics.wait_sum);
+			hierarchy_ws += tg->cfs_rq[i]->hierarchy_wait_sum;
+		}
 
-		seq_printf(sf, "wait_sum %llu\n", ws);
+		seq_printf(sf, "intergroup wait_sum %llu\n", inter_ws);
+		seq_printf(sf, "hierarchy wait_sum %llu\n", hierarchy_ws);
 	}
 
 	return 0;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e2ff4b6..35e89ca 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -858,6 +858,19 @@ static void update_curr_fair(struct rq *rq)
 }
 
 static inline void
+update_hierarchy_wait_sum(struct sched_entity *se,
+			u64 delta_wait)
+{
+	for_each_sched_entity(se) {
+		struct cfs_rq *cfs_rq = cfs_rq_of(se);
+
+		if (cfs_rq->tg != &root_task_group)
+			__schedstat_add(cfs_rq->hierarchy_wait_sum,
+					delta_wait);
+	}
+}
+
+static inline void
 update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	struct task_struct *p;
@@ -880,6 +893,7 @@ static void update_curr_fair(struct rq *rq)
 			return;
 		}
 		trace_sched_stat_wait(p, delta);
+		update_hierarchy_wait_sum(se, delta);
 	}
 
 	__schedstat_set(se->statistics.wait_max,
@@ -10273,6 +10287,9 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
 #ifndef CONFIG_64BIT
 	cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
 #endif
+#ifdef CONFIG_SCHEDSTATS
+	cfs_rq->hierarchy_wait_sum = 0;
+#endif
 #ifdef CONFIG_SMP
 	raw_spin_lock_init(&cfs_rq->removed.lock);
 #endif
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d27c1a5..c01ab99 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -496,6 +496,9 @@ struct cfs_rq {
 #ifndef CONFIG_64BIT
 	u64			min_vruntime_copy;
 #endif
+#ifdef CONFIG_SCHEDSTATS
+	u64			hierarchy_wait_sum;
+#endif
 
 	struct rb_root_cached	tasks_timeline;
 
-- 
1.8.3.1