[PATCH 5.10 002/191] sched/uclamp: Ignore (util == 0) optimization in feec() when p_util_max = 0

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Qais Yousef <qyousef@layalina.io>

[ Upstream commit 23c9519def98ee0fa97ea5871535e9b136f522fc ]

find_energy_efficient_cpu() bails out early if effective util of the
task is 0 as the delta at this point will be zero and there's nothing
for EAS to do. When uclamp is being used, this could lead to wrong
decisions when uclamp_max is set to 0. In this case the task is capped
to performance point 0, but it is actually running and consuming energy
and we can benefit from EAS energy calculations.

Rework the condition so that it bails out when both util and uclamp_min
are 0.

We can do that without needing to use uclamp_task_util(); remove it.

Fixes: d81304bc6193 ("sched/uclamp: Cater for uclamp in find_energy_efficient_cpu()'s early exit condition")
Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230916232955.2099394-3-qyousef@layalina.io
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/sched/fair.c | 18 +-----------------
 1 file changed, 1 insertion(+), 17 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d53f57ac76094..73a89fbd81be8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3927,22 +3927,6 @@ static inline unsigned long task_util_est(struct task_struct *p)
 	return max(task_util(p), _task_util_est(p));
 }
 
-#ifdef CONFIG_UCLAMP_TASK
-static inline unsigned long uclamp_task_util(struct task_struct *p,
-					     unsigned long uclamp_min,
-					     unsigned long uclamp_max)
-{
-	return clamp(task_util_est(p), uclamp_min, uclamp_max);
-}
-#else
-static inline unsigned long uclamp_task_util(struct task_struct *p,
-					     unsigned long uclamp_min,
-					     unsigned long uclamp_max)
-{
-	return task_util_est(p);
-}
-#endif
-
 static inline void util_est_enqueue(struct cfs_rq *cfs_rq,
 				    struct task_struct *p)
 {
@@ -6842,7 +6826,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 		goto fail;
 
 	sync_entity_load_avg(&p->se);
-	if (!uclamp_task_util(p, p_util_min, p_util_max))
+	if (!task_util_est(p) && p_util_min == 0)
 		goto unlock;
 
 	for (; pd; pd = pd->next) {
-- 
2.42.0