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Subject[PATCH] sched/debug: Show intergroup and hierarchy sum wait time of a task group
Date
From: yuzhoujian <yuzhoujian@didichuxing.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@didichuxing.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
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