sched/fair: Don't remove important task migration logic from PELT

This task migration logic is guarded by a WALT #ifdef even though it has
nothing specific to do with WALT. The result is that, with PELT, boosted
tasks can be migrated to the little cluster, causing visible stutters.

Move the WALT #ifdef so PELT can benefit from this logic as well.

Thanks to Zachariah Kennedy <[email protected]> and Danny Lin
<[email protected]> for discovering this issue and creating this fix.

Signed-off-by: Sultan Alsawaf <[email protected]>

kernel/sched/fair.c

@@ -9223,12 +9223,12 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
 	if (env->flags & LBF_IGNORE_PREFERRED_CLUSTER_TASKS &&
 			 !preferred_cluster(cpu_rq(env->dst_cpu)->cluster, p))
 		return 0;
+#endif
 
 	/* Don't detach task if it doesn't fit on the destination */
 	if (env->flags & LBF_IGNORE_BIG_TASKS &&
 		!task_fits_max(p, env->dst_cpu))
 		return 0;
-#endif
 
 	if (task_running(env->src_rq, p)) {
 		schedstat_inc(p->se.statistics.nr_failed_migrations_running);