sched/fair: optimize the PLACE_LAG when se->vlag is zero

When PLACE_LAG is enabled, from the relationship:
            vl_i = (W + w_i)*vl'_i / W
we know that if vl'_i(se->vlag) is zero, the vl_i is zero too.

So if se->vlag is zero, there is no need to waste cycles to
do the calculation.

Signed-off-by: Huang Shijie <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Christoph Lameter (Ampere) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: HuangShijie2024

kernel/sched/fair.c

@@ -5280,7 +5280,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	 *
 	 * EEVDF: placement strategy #1 / #2
 	 */
-	if (sched_feat(PLACE_LAG) && cfs_rq->nr_running) {
+	if (sched_feat(PLACE_LAG) && cfs_rq->nr_running && se->vlag) {
 		struct sched_entity *curr = cfs_rq->curr;
 		unsigned long load;