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Message-Id: <1608344449-3149-1-git-send-email-xuewen.yan94@gmail.com>
Date: Sat, 19 Dec 2020 10:20:49 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: dietmar.eggemann@....com, vincent.guittot@...aro.org,
juri.lelli@...hat.com, peterz@...radead.org, mingo@...hat.com
Cc: rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
bristot@...hat.com, linux-kernel@...r.kernel.org,
patrick.bellasi@....com, zhang.lyra@...il.com, Ke.Wang@...soc.com,
xuewyan@...mail.com, Xuewen.Yan@...soc.com
Subject: [PATCH v4] sched/fair: Avoid stale CPU util_est value for schedutil in task dequeue
From: Xuewen Yan <xuewen.yan@...soc.com>
CPU (root cfs_rq) estimated utilization (util_est) is currently used in
dequeue_task_fair() to drive frequency selection before it is updated.
with:
CPU_util : rq->cfs.avg.util_avg
CPU_util_est : rq->cfs.avg.util_est
CPU_utilization : max(CPU_util, CPU_util_est)
task_util : p->se.avg.util_avg
task_util_est : p->se.avg.util_est
dequeue_task_fair():
/* (1) CPU_util and task_util update + inform schedutil about
CPU_utilization changes */
for_each_sched_entity() /* 2 loops */
(dequeue_entity() ->) update_load_avg() -> cfs_rq_util_change()
-> cpufreq_update_util() ->...-> sugov_update_[shared\|single]
-> sugov_get_util() -> cpu_util_cfs()
/* (2) CPU_util_est and task_util_est update */
util_est_dequeue()
cpu_util_cfs() uses CPU_utilization which could lead to a false (too
high) utilization value for schedutil in task ramp-down or ramp-up
scenarios during task dequeue.
To mitigate the issue split the util_est update (2) into:
(A) CPU_util_est update in util_est_dequeue()
(B) task_util_est update in util_est_update()
Place (A) before (1) and keep (B) where (2) is. The latter is necessary
since (B) relies on task_util update in (1).
Fixes: 7f65ea42eb00 ("sched/fair: Add util_est on top of PELT")
Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
---
Change since v3:
-add reviewer
-add more comment details
Changes since v2:
-modify the comment
-move util_est_dequeue above within_margin()
-modify the tab and space
Changes since v1:
-change the util_est_dequeue/update to inline type
-use unsigned int enqueued rather than util_est in util_est_dequeue
-remove "cpu" var
---
kernel/sched/fair.c | 43 ++++++++++++++++++++++++++++---------------
1 file changed, 28 insertions(+), 15 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ae7ceba..f3a1b7a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3932,6 +3932,22 @@ static inline void util_est_enqueue(struct cfs_rq *cfs_rq,
trace_sched_util_est_cfs_tp(cfs_rq);
}
+static inline void util_est_dequeue(struct cfs_rq *cfs_rq,
+ struct task_struct *p)
+{
+ unsigned int enqueued;
+
+ if (!sched_feat(UTIL_EST))
+ return;
+
+ /* Update root cfs_rq's estimated utilization */
+ enqueued = cfs_rq->avg.util_est.enqueued;
+ enqueued -= min_t(unsigned int, enqueued, _task_util_est(p));
+ WRITE_ONCE(cfs_rq->avg.util_est.enqueued, enqueued);
+
+ trace_sched_util_est_cfs_tp(cfs_rq);
+}
+
/*
* Check if a (signed) value is within a specified (unsigned) margin,
* based on the observation that:
@@ -3945,23 +3961,16 @@ static inline bool within_margin(int value, int margin)
return ((unsigned int)(value + margin - 1) < (2 * margin - 1));
}
-static void
-util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p, bool task_sleep)
+static inline void util_est_update(struct cfs_rq *cfs_rq,
+ struct task_struct *p,
+ bool task_sleep)
{
long last_ewma_diff;
struct util_est ue;
- int cpu;
if (!sched_feat(UTIL_EST))
return;
- /* Update root cfs_rq's estimated utilization */
- ue.enqueued = cfs_rq->avg.util_est.enqueued;
- ue.enqueued -= min_t(unsigned int, ue.enqueued, _task_util_est(p));
- WRITE_ONCE(cfs_rq->avg.util_est.enqueued, ue.enqueued);
-
- trace_sched_util_est_cfs_tp(cfs_rq);
-
/*
* Skip update of task's estimated utilization when the task has not
* yet completed an activation, e.g. being migrated.
@@ -4001,8 +4010,7 @@ static inline bool within_margin(int value, int margin)
* To avoid overestimation of actual task utilization, skip updates if
* we cannot grant there is idle time in this CPU.
*/
- cpu = cpu_of(rq_of(cfs_rq));
- if (task_util(p) > capacity_orig_of(cpu))
+ if (task_util(p) > capacity_orig_of(cpu_of(rq_of(cfs_rq))))
return;
/*
@@ -4085,8 +4093,11 @@ static inline int newidle_balance(struct rq *rq, struct rq_flags *rf)
util_est_enqueue(struct cfs_rq *cfs_rq, struct task_struct *p) {}
static inline void
-util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p,
- bool task_sleep) {}
+util_est_dequeue(struct cfs_rq *cfs_rq, struct task_struct *p) {}
+
+static inline void
+util_est_update(struct cfs_rq *cfs_rq, struct task_struct *p,
+ bool task_sleep) {}
static inline void update_misfit_status(struct task_struct *p, struct rq *rq) {}
#endif /* CONFIG_SMP */
@@ -5589,6 +5600,8 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
int idle_h_nr_running = task_has_idle_policy(p);
bool was_sched_idle = sched_idle_rq(rq);
+ util_est_dequeue(&rq->cfs, p);
+
for_each_sched_entity(se) {
cfs_rq = cfs_rq_of(se);
dequeue_entity(cfs_rq, se, flags);
@@ -5639,7 +5652,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
rq->next_balance = jiffies;
dequeue_throttle:
- util_est_dequeue(&rq->cfs, p, task_sleep);
+ util_est_update(&rq->cfs, p, task_sleep);
hrtick_update(rq);
}
--
1.9.1
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