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Message-Id: <20190628204913.10287-6-riel@surriel.com>
Date: Fri, 28 Jun 2019 16:49:08 -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 05/10] sched,fair: remove cfs rqs from leaf_cfs_rq_list bottom up
Reducing the overhead of the CPU controller is achieved by not walking
all the sched_entities every time a task is enqueued or dequeued.
One of the things being checked every single time is whether the cfs_rq
is on the rq->leaf_cfs_rq_list.
By only removing a cfs_rq from the list once it no longer has children
on the list, we can avoid walking the sched_entity hierarchy if the bottom
cfs_rq is on the list, once the runqueues have been flattened.
Signed-off-by: Rik van Riel <riel@...riel.com>
---
kernel/sched/fair.c | 17 +++++++++++++++++
kernel/sched/sched.h | 1 +
2 files changed, 18 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 63cb40253b26..e41feacc45d9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -286,6 +286,13 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
cfs_rq->on_list = 1;
+ /*
+ * If the tmp_alone_branch cursor was moved, it means a child cfs_rq
+ * is already on the list ahead of us.
+ */
+ if (rq->tmp_alone_branch != &rq->leaf_cfs_rq_list)
+ cfs_rq->children_on_list++;
+
/*
* Ensure we either appear before our parent (if already
* enqueued) or force our parent to appear after us when it is
@@ -311,6 +318,7 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
* list.
*/
rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
+ cfs_rq->tg->parent->cfs_rq[cpu]->children_on_list++;
return true;
}
@@ -359,6 +367,11 @@ static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
if (rq->tmp_alone_branch == &cfs_rq->leaf_cfs_rq_list)
rq->tmp_alone_branch = cfs_rq->leaf_cfs_rq_list.prev;
+ if (cfs_rq->tg->parent) {
+ int cpu = cpu_of(rq);
+ cfs_rq->tg->parent->cfs_rq[cpu]->children_on_list--;
+ }
+
list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
cfs_rq->on_list = 0;
}
@@ -7687,6 +7700,10 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
if (cfs_rq->avg.util_sum)
return false;
+ /* Remove decayed parents once their decayed children are gone. */
+ if (cfs_rq->children_on_list)
+ return false;
+
return true;
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 32978a8de8ce..4f8acbab0fb2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -557,6 +557,7 @@ struct cfs_rq {
* This list is used during load balance.
*/
int on_list;
+ int children_on_list;
struct list_head leaf_cfs_rq_list;
struct task_group *tg; /* group that "owns" this runqueue */
--
2.20.1
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