sched/core: Kill sched_class::task_waking to clean up the migration logic

With sched_class::task_waking being called only when we do
set_task_cpu(), we can make sched_class::migrate_task_rq() do the work
and eliminate sched_class::task_waking entirely.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Hunter <ahh@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Paul Turner <pjt@google.com>
Cc: Pavan Kondeti <pkondeti@codeaurora.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: byungchul.park@lge.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 32 insertions, 42 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1f73e2554bc1..636c4b9cac38 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1717,11 +1717,8 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
         if (p->sched_contributes_to_load)
                 rq->nr_uninterruptible--;
 
-        /*
-         * If we migrated; we must have called sched_class::task_waking().
-         */
         if (wake_flags & WF_MIGRATED)
-                en_flags |= ENQUEUE_WAKING;
+                en_flags |= ENQUEUE_MIGRATED;
 #endif
 
         ttwu_activate(rq, p, en_flags);
@@ -2049,10 +2046,6 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
         cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags);
         if (task_cpu(p) != cpu) {
                 wake_flags |= WF_MIGRATED;
-
-                if (p->sched_class->task_waking)
-                        p->sched_class->task_waking(p);
-
                 set_task_cpu(p, cpu);
         }
 #endif /* CONFIG_SMP */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 445bcd2d7ee1..24ce01b73906 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3273,7 +3273,7 @@ static inline void check_schedstat_required(void)
  *
  * WAKEUP (remote)
  *
- *      ->task_waking_fair()
+ *      ->migrate_task_rq_fair() (p->state == TASK_WAKING)
  *        vruntime -= min_vruntime
  *
  *      enqueue
@@ -3292,7 +3292,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
          * Update the normalized vruntime before updating min_vruntime
          * through calling update_curr().
          */
-        if (!(flags & ENQUEUE_WAKEUP) || (flags & ENQUEUE_WAKING))
+        if (!(flags & ENQUEUE_WAKEUP) || (flags & ENQUEUE_MIGRATED))
                 se->vruntime += cfs_rq->min_vruntime;
 
         /*
@@ -4841,33 +4841,6 @@ static unsigned long cpu_avg_load_per_task(int cpu)
         return 0;
 }
 
-/*
- * Called to migrate a waking task; as blocked tasks retain absolute vruntime
- * the migration needs to deal with this by subtracting the old and adding the
- * new min_vruntime -- the latter is done by enqueue_entity() when placing
- * the task on the new runqueue.
- */
-static void task_waking_fair(struct task_struct *p)
-{
-        struct sched_entity *se = &p->se;
-        struct cfs_rq *cfs_rq = cfs_rq_of(se);
-        u64 min_vruntime;
-
-#ifndef CONFIG_64BIT
-        u64 min_vruntime_copy;
-
-        do {
-                min_vruntime_copy = cfs_rq->min_vruntime_copy;
-                smp_rmb();
-                min_vruntime = cfs_rq->min_vruntime;
-        } while (min_vruntime != min_vruntime_copy);
-#else
-        min_vruntime = cfs_rq->min_vruntime;
-#endif
-
-        se->vruntime -= min_vruntime;
-}
-
 #ifdef CONFIG_FAIR_GROUP_SCHED
 /*
  * effective_load() calculates the load change as seen from the root_task_group
@@ -5403,6 +5376,32 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
 static void migrate_task_rq_fair(struct task_struct *p)
 {
         /*
+         * As blocked tasks retain absolute vruntime the migration needs to
+         * deal with this by subtracting the old and adding the new
+         * min_vruntime -- the latter is done by enqueue_entity() when placing
+         * the task on the new runqueue.
+         */
+        if (p->state == TASK_WAKING) {
+                struct sched_entity *se = &p->se;
+                struct cfs_rq *cfs_rq = cfs_rq_of(se);
+                u64 min_vruntime;
+
+#ifndef CONFIG_64BIT
+                u64 min_vruntime_copy;
+
+                do {
+                        min_vruntime_copy = cfs_rq->min_vruntime_copy;
+                        smp_rmb();
+                        min_vruntime = cfs_rq->min_vruntime;
+                } while (min_vruntime != min_vruntime_copy);
+#else
+                min_vruntime = cfs_rq->min_vruntime;
+#endif
+
+                se->vruntime -= min_vruntime;
+        }
+
+        /*
          * We are supposed to update the task to "current" time, then its up to date
          * and ready to go to new CPU/cfs_rq. But we have difficulty in getting
          * what current time is, so simply throw away the out-of-date time. This
@@ -8672,7 +8671,6 @@ const struct sched_class fair_sched_class = {
         .rq_online              = rq_online_fair,
         .rq_offline             = rq_offline_fair,
 
-        .task_waking            = task_waking_fair,
         .task_dead              = task_dead_fair,
         .set_cpus_allowed       = set_cpus_allowed_common,
 #endif
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ab6adb159e23..e51145e76807 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1168,7 +1168,7 @@ extern const u32 sched_prio_to_wmult[40];
  *
  * ENQUEUE_HEAD      - place at front of runqueue (tail if not specified)
  * ENQUEUE_REPLENISH - CBS (replenish runtime and postpone deadline)
- * ENQUEUE_WAKING    - sched_class::task_waking was called
+ * ENQUEUE_MIGRATED  - the task was migrated during wakeup
  *
  */
 
@@ -1183,9 +1183,9 @@ extern const u32 sched_prio_to_wmult[40];
 #define ENQUEUE_HEAD            0x08
 #define ENQUEUE_REPLENISH       0x10
 #ifdef CONFIG_SMP
-#define ENQUEUE_WAKING          0x20
+#define ENQUEUE_MIGRATED        0x20
 #else
-#define ENQUEUE_WAKING          0x00
+#define ENQUEUE_MIGRATED        0x00
 #endif
 
 #define RETRY_TASK              ((void *)-1UL)
@@ -1217,7 +1217,6 @@ struct sched_class {
         int  (*select_task_rq)(struct task_struct *p, int task_cpu, int sd_flag, int flags);
         void (*migrate_task_rq)(struct task_struct *p);
 
-        void (*task_waking) (struct task_struct *task);
         void (*task_woken) (struct rq *this_rq, struct task_struct *task);
 
         void (*set_cpus_allowed)(struct task_struct *p,