[PATCH 2/4] sched/eevdf: Update se->vprot in reweight_entity()

[Peter Zijlstra]

From: Wang Tao <wangtao554@xxxxxxxxxx>

In the EEVDF framework with Run-to-Parity protection, `se->vprot` is an
independent variable defining the virtual protection timestamp.

When `reweight_entity()` is called (e.g., via nice/renice), it performs
the following actions to preserve Lag consistency:
 1. Scales `se->vlag` based on the new weight.
 2. Calls `place_entity()`, which recalculates `se->vruntime` based on
    the new weight and scaled lag.

However, the current implementation fails to update `se->vprot`, leading
to mismatches between the task's actual runtime and its expected duration.

Fixes: 63304558ba5d ("sched/eevdf: Curb wakeup-preemption")
Suggested-by: Zhang Qiao <zhangqiao22@xxxxxxxxxx>
Signed-off-by: Wang Tao <wangtao554@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260120123113.3518950-1-wangtao554@xxxxxxxxxx
---
 kernel/sched/fair.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3790,6 +3790,8 @@ static void reweight_entity(struct cfs_r
 			    unsigned long weight)
 {
 	bool curr = cfs_rq->curr == se;
+	bool rel_vprot = false;
+	u64 vprot;
 
 	if (se->on_rq) {
 		/* commit outstanding execution time */
@@ -3797,6 +3799,11 @@ static void reweight_entity(struct cfs_r
 		update_entity_lag(cfs_rq, se);
 		se->deadline -= se->vruntime;
 		se->rel_deadline = 1;
+		if (curr && protect_slice(se)) {
+			vprot = se->vprot - se->vruntime;
+			rel_vprot = true;
+		}
+
 		cfs_rq->nr_queued--;
 		if (!curr)
 			__dequeue_entity(cfs_rq, se);
@@ -3812,6 +3819,9 @@ static void reweight_entity(struct cfs_r
 	if (se->rel_deadline)
 		se->deadline = div_s64(se->deadline * se->load.weight, weight);
 
+	if (rel_vprot)
+		vprot = div_s64(vprot * se->load.weight, weight);
+
 	update_load_set(&se->load, weight);
 
 	do {
@@ -3823,6 +3833,8 @@ static void reweight_entity(struct cfs_r
 	enqueue_load_avg(cfs_rq, se);
 	if (se->on_rq) {
 		place_entity(cfs_rq, se, 0);
+		if (rel_vprot)
+			se->vprot = se->vruntime + vprot;
 		update_load_add(&cfs_rq->load, se->load.weight);
 		if (!curr)
 			__enqueue_entity(cfs_rq, se);