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sched/fair: Fix pelt lost idle time detection

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[ Upstream commit 17e3e88ed0 ]

The check for some lost idle pelt time should be always done when
pick_next_task_fair() fails to pick a task and not only when we call it
from the fair fast-path.

The case happens when the last running task on rq is a RT or DL task. When
the latter goes to sleep and the /Sum of util_sum of the rq is at the max
value, we don't account the lost of idle time whereas we should.

Fixes: 67692435c4 ("sched: Rework pick_next_task() slow-path")
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Vincent Guittot 2025-10-08 15:12:14 +02:00 committed by Greg Kroah-Hartman
parent ab6c0f1585
commit 13aeb56dae
1 changed files with 13 additions and 13 deletions
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26
kernel/sched/fair.c
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@ -8829,21 +8829,21 @@ simple:
return p; return p;
idle: idle:
if (!rf) if (rf) {
return NULL; new_tasks = sched_balance_newidle(rq, rf);
new_tasks = sched_balance_newidle(rq, rf); /*
* Because sched_balance_newidle() releases (and re-acquires)
* rq->lock, it is possible for any higher priority task to
* appear. In that case we must re-start the pick_next_entity()
* loop.
*/
if (new_tasks < 0)
return RETRY_TASK;
/* if (new_tasks > 0)
* Because sched_balance_newidle() releases (and re-acquires) rq->lock, it is goto again;
* possible for any higher priority task to appear. In that case we }
* must re-start the pick_next_entity() loop.
*/
if (new_tasks < 0)
return RETRY_TASK;
if (new_tasks > 0)
goto again;
/* /*
* rq is about to be idle, check if we need to update the * rq is about to be idle, check if we need to update the