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Subject[RFC PATCH v2 3/5] sched/fair: Delete cfs_rq_throttled_loose(), use cfs_rq->throttle_pending instead
Date
cfs_rq_throttled_loose() does not check if there is runtime remaining in
the cfs_b, and thus relies on check_cfs_rq_runtime() being ran previously
for that to be checked.

Cache the throttle attempt in throttle_cfs_rq and reuse that where
needed.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
kernel/sched/fair.c | 44 ++++++++++----------------------------------
1 file changed, 10 insertions(+), 34 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 96504be6ee14a..60778afbff207 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5462,7 +5462,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
* 5) do not run the "skip" process, if something else is available
*/
static struct sched_entity *
-pick_next_entity(struct cfs_rq *cfs_rq, bool throttled)
+pick_next_entity(struct cfs_rq *cfs_rq)
{
#ifdef CONFIG_CFS_BANDWIDTH
/*
@@ -5473,7 +5473,7 @@ pick_next_entity(struct cfs_rq *cfs_rq, bool throttled)
* throttle_cfs_rq.
*/
WARN_ON_ONCE(list_empty(&cfs_rq->kernel_children));
- if (throttled && !list_empty(&cfs_rq->kernel_children)) {
+ if (cfs_rq->throttle_pending && !list_empty(&cfs_rq->kernel_children)) {
/*
* TODO: you'd want to factor out pick_eevdf to just take
* tasks_timeline, and replace this list with a second rbtree
@@ -5791,8 +5791,12 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
* We don't actually throttle, though account() will have made sure to
* resched us so that we pick into a kernel task.
*/
- if (cfs_rq->h_kernel_running)
+ if (cfs_rq->h_kernel_running) {
+ cfs_rq->throttle_pending = true;
return false;
+ }
+
+ cfs_rq->throttle_pending = false;

raw_spin_lock(&cfs_b->lock);
/* This will start the period timer if necessary */
@@ -6666,20 +6670,6 @@ static void dequeue_kernel(struct cfs_rq *cfs_rq, struct sched_entity *se, int c
cfs_rq->h_kernel_running -= count;
}

-/*
- * Returns if the cfs_rq "should" be throttled but might not be because of
- * kernel threads bypassing throttle.
- */
-static bool cfs_rq_throttled_loose(struct cfs_rq *cfs_rq)
-{
- if (!cfs_bandwidth_used())
- return false;
-
- if (likely(!cfs_rq->runtime_enabled || cfs_rq->runtime_remaining > 0))
- return false;
- return true;
-}
-
static void unthrottle_on_enqueue(struct task_struct *p)
{
struct sched_entity *se = &p->se;
@@ -8546,7 +8536,6 @@ static struct task_struct *pick_task_fair(struct rq *rq)
{
struct sched_entity *se;
struct cfs_rq *cfs_rq;
- bool throttled = false;

again:
cfs_rq = &rq->cfs;
@@ -8567,10 +8556,7 @@ static struct task_struct *pick_task_fair(struct rq *rq)
goto again;
}

- if (cfs_rq_throttled_loose(cfs_rq))
- throttled = true;
-
- se = pick_next_entity(cfs_rq, throttled);
+ se = pick_next_entity(cfs_rq);
cfs_rq = group_cfs_rq(se);
} while (cfs_rq);

@@ -8585,7 +8571,6 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
struct sched_entity *se;
struct task_struct *p;
int new_tasks;
- bool throttled;

/*
* We want to handle this before check_cfs_runtime(prev). We'll
@@ -8609,8 +8594,6 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
* Therefore attempt to avoid putting and setting the entire cgroup
* hierarchy, only change the part that actually changes.
*/
-
- throttled = false;
do {
struct sched_entity *curr = cfs_rq->curr;

@@ -8641,11 +8624,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
goto simple;
}
}
-
- if (cfs_rq_throttled_loose(cfs_rq))
- throttled = true;
-
- se = pick_next_entity(cfs_rq, throttled);
+ se = pick_next_entity(cfs_rq);
cfs_rq = group_cfs_rq(se);
} while (cfs_rq);

@@ -8683,11 +8662,8 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
if (prev)
put_prev_task(rq, prev);

- throttled = false;
do {
- if (cfs_rq_throttled_loose(cfs_rq))
- throttled = true;
- se = pick_next_entity(cfs_rq, throttled);
+ se = pick_next_entity(cfs_rq);
set_next_entity(cfs_rq, se);
cfs_rq = group_cfs_rq(se);
} while (cfs_rq);
--
2.43.0

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