linux-kernel - [PATCH v5 2/3] sched/fair: Add cfs bandwidth burst statistics

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Date:   Thu, 20 May 2021 20:34:18 +0800
From:   Huaixin Chang <changhuaixin@...ux.alibaba.com>
To:     changhuaixin@...ux.alibaba.com
Cc:     bsegall@...gle.com, dietmar.eggemann@....com,
        dtcccc@...ux.alibaba.com, juri.lelli@...hat.com,
        khlebnikov@...dex-team.ru, linux-kernel@...r.kernel.org,
        mgorman@...e.de, mingo@...hat.com, odin@...d.al, odin@...dal.com,
        pauld@...head.com, peterz@...radead.org, pjt@...gle.com,
        rostedt@...dmis.org, shanpeic@...ux.alibaba.com, tj@...nel.org,
        vincent.guittot@...aro.org, xiyou.wangcong@...il.com
Subject: [PATCH v5 2/3] sched/fair: Add cfs bandwidth burst statistics

When using cfs_b and meeting with some throttled periods, users shall
use burst buffer to allow bursty workloads. Apart from configuring some
burst buffer and watch whether throttled periods disappears, some
statistics on burst buffer using are also helpful. Thus expose the
following statistics into cpu.stat file:

nr_burst:   number of periods bandwidth burst occurs
burst_time: cumulative wall-time that any cpus has
	    used above quota in respective periods

Co-developed-by: Shanpei Chen <shanpeic@...ux.alibaba.com>
Signed-off-by: Shanpei Chen <shanpeic@...ux.alibaba.com>
Co-developed-by: Tianchen Ding <dtcccc@...ux.alibaba.com>
Signed-off-by: Tianchen Ding <dtcccc@...ux.alibaba.com>
Signed-off-by: Huaixin Chang <changhuaixin@...ux.alibaba.com>
---
 kernel/sched/core.c  | 13 ++++++++++---
 kernel/sched/fair.c  | 11 +++++++++++
 kernel/sched/sched.h |  3 +++
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7d34b08ee0e5..d442fcd85374 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9265,6 +9265,9 @@ static int cpu_cfs_stat_show(struct seq_file *sf, void *v)
 		seq_printf(sf, "wait_sum %llu\n", ws);
 	}
 
+	seq_printf(sf, "nr_burst %d\n", cfs_b->nr_burst);
+	seq_printf(sf, "burst_time %llu\n", cfs_b->burst_time);
+
 	return 0;
 }
 #endif /* CONFIG_CFS_BANDWIDTH */
@@ -9361,16 +9364,20 @@ static int cpu_extra_stat_show(struct seq_file *sf,
 	{
 		struct task_group *tg = css_tg(css);
 		struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
-		u64 throttled_usec;
+		u64 throttled_usec, burst_usec;
 
 		throttled_usec = cfs_b->throttled_time;
 		do_div(throttled_usec, NSEC_PER_USEC);
+		burst_usec = cfs_b->burst_time;
+		do_div(burst_usec, NSEC_PER_USEC);
 
 		seq_printf(sf, "nr_periods %d\n"
 			   "nr_throttled %d\n"
-			   "throttled_usec %llu\n",
+			   "throttled_usec %llu\n"
+			   "nr_burst %d\n"
+			   "burst_usec %llu\n",
 			   cfs_b->nr_periods, cfs_b->nr_throttled,
-			   throttled_usec);
+			   throttled_usec, cfs_b->nr_burst, burst_usec);
 	}
 #endif
 	return 0;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 48fad5cf0f7a..d4783b62a010 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4635,6 +4635,8 @@ static inline u64 sched_cfs_bandwidth_slice(void)
  */
 void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
 {
+	u64 runtime;
+
 	if (unlikely(cfs_b->quota == RUNTIME_INF))
 		return;
 
@@ -4643,8 +4645,17 @@ void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
 		return;
 	}
 
+	if (cfs_b->runtime_at_period_start > cfs_b->runtime) {
+		runtime = cfs_b->runtime_at_period_start - cfs_b->runtime;
+		if (runtime > cfs_b->quota) {
+			cfs_b->burst_time += runtime - cfs_b->quota;
+			cfs_b->nr_burst++;
+		}
+	}
+
 	cfs_b->runtime += cfs_b->quota;
 	cfs_b->runtime = min(cfs_b->runtime, cfs_b->quota + cfs_b->burst);
+	cfs_b->runtime_at_period_start = cfs_b->runtime;
 }
 
 static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d317ca74a48c..b770b553dfbb 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -367,6 +367,7 @@ struct cfs_bandwidth {
 	u64			quota;
 	u64			runtime;
 	u64			burst;
+	u64			runtime_at_period_start;
 	s64			hierarchical_quota;
 
 	u8			idle;
@@ -379,7 +380,9 @@ struct cfs_bandwidth {
 	/* Statistics: */
 	int			nr_periods;
 	int			nr_throttled;
+	int			nr_burst;
 	u64			throttled_time;
+	u64			burst_time;
 #endif
 };
 
-- 
2.14.4.44.g2045bb6