linux-kernel - [PATCH 14/15] sched,fair: ramp up task_se_h

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Message-Id: <20190822021740.15554-15-riel@surriel.com>
Date:   Wed, 21 Aug 2019 22:17:39 -0400
From:   Rik van Riel <riel@...riel.com>
To:     linux-kernel@...r.kernel.org
Cc:     kernel-team@...com, pjt@...gle.com, dietmar.eggemann@....com,
        peterz@...radead.org, mingo@...hat.com, morten.rasmussen@....com,
        tglx@...utronix.de, mgorman@...hsingularity.net,
        vincent.guittot@...aro.org, Rik van Riel <riel@...riel.com>
Subject: [PATCH 14/15] sched,fair: ramp up task_se_h_weight quickly

The code in update_cfs_group / calc_group_shares has some logic to
quickly ramp up the load when a task has just started running in a
cgroup, in order to get sane values for the cgroup se->load.weight.

This code adds a similar hack to task_se_h_weight.

However, THIS CODE IS WRONG, since it does not do things hierarchically.

I am wondering a few things here:
1) Should I have something similar to the logic in calc_group_shares
   in update_cfs_rq_h_load?
2) If so, should I also use that fast-ramp-up value for task_h_load,
   to prevent the load balancer from thinking it is moving zero weight
   tasks around?
3) If update_cfs_rq_h_load is the wrong place, where should I be
   calculating a hierarchical group weight value, instead?

Not-yet-signed-off-by: Rik van Riel <riel@...riel.com>
Signed-off-by: Rik van Riel <riel@...riel.com>
---
 kernel/sched/fair.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d6c881c5c4d5..3df5d60b245f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7672,6 +7672,7 @@ static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)

 static unsigned long task_se_h_weight(struct sched_entity *se)
 {
+	unsigned long group_load;
 	struct cfs_rq *cfs_rq;

 	if (!task_se_in_cgroup(se))
@@ -7680,8 +7681,12 @@ static unsigned long task_se_h_weight(struct sched_entity *se)
 	cfs_rq = group_cfs_rq_of_parent(se);
 	update_cfs_rq_h_load(cfs_rq);

+	/* Ramp up quickly to keep h_weight sane. */
+	group_load = max(scale_load_down(se->parent->load.weight),
+							cfs_rq->h_load);
+
 	/* Reduce the load.weight by the h_load of the group the task is in. */
-	return (cfs_rq->h_load * se->load.weight) >> SCHED_FIXEDPOINT_SHIFT;
+	return (group_load * se->load.weight) >> SCHED_FIXEDPOINT_SHIFT;
 }

 static unsigned long task_se_h_load(struct sched_entity *se)
-- 
2.20.1