sched/fair: Implement ENQUEUE_DELAYED

Doing a wakeup on a delayed dequeue task is about as simple as it
sounds -- remove the delayed mark and enjoy the fact it was actually
still on the runqueue.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lkml.kernel.org/r/20240727105029.888107381@infradead.org

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a4f1f79ac90c12d8c044004eb9da97dfb5b0da69..25b14dffeb37ba62a46031709e72b807e8f50e93 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5289,6 +5289,9 @@ static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq);
 
 static inline bool cfs_bandwidth_used(void);
 
+static void
+requeue_delayed_entity(struct sched_entity *se);
+
 static void
 enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
@@ -5922,8 +5925,10 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
        for_each_sched_entity(se) {
                struct cfs_rq *qcfs_rq = cfs_rq_of(se);
 
-               if (se->on_rq)
+               if (se->on_rq) {
+                       SCHED_WARN_ON(se->sched_delayed);
                        break;
+               }
                enqueue_entity(qcfs_rq, se, ENQUEUE_WAKEUP);
 
                if (cfs_rq_is_idle(group_cfs_rq(se)))
@@ -6773,6 +6778,22 @@ static int sched_idle_cpu(int cpu)
 }
 #endif
 
+static void
+requeue_delayed_entity(struct sched_entity *se)
+{
+       struct cfs_rq *cfs_rq = cfs_rq_of(se);
+
+       /*
+        * se->sched_delayed should imply: se->on_rq == 1.
+        * Because a delayed entity is one that is still on
+        * the runqueue competing until elegibility.
+        */
+       SCHED_WARN_ON(!se->sched_delayed);
+       SCHED_WARN_ON(!se->on_rq);
+
+       se->sched_delayed = 0;
+}
+
 /*
  * The enqueue_task method is called before nr_running is
  * increased. Here we update the fair scheduling stats and
@@ -6787,6 +6808,11 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
        int task_new = !(flags & ENQUEUE_WAKEUP);
        int rq_h_nr_running = rq->cfs.h_nr_running;
 
+       if (flags & ENQUEUE_DELAYED) {
+               requeue_delayed_entity(se);
+               return;
+       }
+
        /*
         * The code below (indirectly) updates schedutil which looks at
         * the cfs_rq utilization to select a frequency.
@@ -6804,8 +6830,11 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
                cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
 
        for_each_sched_entity(se) {
-               if (se->on_rq)
+               if (se->on_rq) {
+                       if (se->sched_delayed)
+                               requeue_delayed_entity(se);
                        break;
+               }
                cfs_rq = cfs_rq_of(se);
                enqueue_entity(cfs_rq, se, flags);