sched: Introduce sched_class::pick_task()

Because sched_class::pick_next_task() also implies
sched_class::set_next_task() (and possibly put_prev_task() and
newidle_balance) it is not state invariant. This makes it unsuitable
for remote task selection.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[Vineeth: folded fixes]
Signed-off-by: Vineeth Remanan Pillai <viremana@linux.microsoft.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Don Hiatt <dhiatt@digitalocean.com>
Tested-by: Hongyu Ning <hongyu.ning@linux.intel.com>
Tested-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20210422123308.437092775@infradead.org

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fb0eb9a..3829c5a 100644 (file)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1852,7 +1852,7 @@ static struct sched_dl_entity *pick_next_dl_entity(struct rq *rq,
        return rb_entry(left, struct sched_dl_entity, rb_node);
 }
 
-static struct task_struct *pick_next_task_dl(struct rq *rq)
+static struct task_struct *pick_task_dl(struct rq *rq)
 {
        struct sched_dl_entity *dl_se;
        struct dl_rq *dl_rq = &rq->dl;
@@ -1864,7 +1864,18 @@ static struct task_struct *pick_next_task_dl(struct rq *rq)
        dl_se = pick_next_dl_entity(rq, dl_rq);
        BUG_ON(!dl_se);
        p = dl_task_of(dl_se);
-       set_next_task_dl(rq, p, true);
+
+       return p;
+}
+
+static struct task_struct *pick_next_task_dl(struct rq *rq)
+{
+       struct task_struct *p;
+
+       p = pick_task_dl(rq);
+       if (p)
+               set_next_task_dl(rq, p, true);
+
        return p;
 }
 
@@ -2539,6 +2550,7 @@ DEFINE_SCHED_CLASS(dl) = {
 
 #ifdef CONFIG_SMP
        .balance                = balance_dl,
+       .pick_task              = pick_task_dl,
        .select_task_rq         = select_task_rq_dl,
        .migrate_task_rq        = migrate_task_rq_dl,
        .set_cpus_allowed       = set_cpus_allowed_dl,

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 18960d0..51d72ab 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4419,6 +4419,8 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
 static void
 set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+       clear_buddies(cfs_rq, se);
+
        /* 'current' is not kept within the tree. */
        if (se->on_rq) {
                /*
@@ -4478,7 +4480,7 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
         * Avoid running the skip buddy, if running something else can
         * be done without getting too unfair.
         */
-       if (cfs_rq->skip == se) {
+       if (cfs_rq->skip && cfs_rq->skip == se) {
                struct sched_entity *second;
 
                if (se == curr) {
@@ -4505,8 +4507,6 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
                se = cfs_rq->last;
        }
 
-       clear_buddies(cfs_rq, se);
-
        return se;
 }
 
@@ -7095,6 +7095,39 @@ preempt:
                set_last_buddy(se);
 }
 
+#ifdef CONFIG_SMP
+static struct task_struct *pick_task_fair(struct rq *rq)
+{
+       struct sched_entity *se;
+       struct cfs_rq *cfs_rq;
+
+again:
+       cfs_rq = &rq->cfs;
+       if (!cfs_rq->nr_running)
+               return NULL;
+
+       do {
+               struct sched_entity *curr = cfs_rq->curr;
+
+               /* When we pick for a remote RQ, we'll not have done put_prev_entity() */
+               if (curr) {
+                       if (curr->on_rq)
+                               update_curr(cfs_rq);
+                       else
+                               curr = NULL;
+
+                       if (unlikely(check_cfs_rq_runtime(cfs_rq)))
+                               goto again;
+               }
+
+               se = pick_next_entity(cfs_rq, curr);
+               cfs_rq = group_cfs_rq(se);
+       } while (cfs_rq);
+
+       return task_of(se);
+}
+#endif
+
 struct task_struct *
 pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 {
@@ -11298,6 +11331,7 @@ DEFINE_SCHED_CLASS(fair) = {
 
 #ifdef CONFIG_SMP
        .balance                = balance_fair,
+       .pick_task              = pick_task_fair,
        .select_task_rq         = select_task_rq_fair,
        .migrate_task_rq        = migrate_task_rq_fair,
 

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 0194768..43646e7 100644 (file)
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -439,6 +439,13 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool fir
        schedstat_inc(rq->sched_goidle);
 }
 
+#ifdef CONFIG_SMP
+static struct task_struct *pick_task_idle(struct rq *rq)
+{
+       return rq->idle;
+}
+#endif
+
 struct task_struct *pick_next_task_idle(struct rq *rq)
 {
        struct task_struct *next = rq->idle;
@@ -506,6 +513,7 @@ DEFINE_SCHED_CLASS(idle) = {
 
 #ifdef CONFIG_SMP
        .balance                = balance_idle,
+       .pick_task              = pick_task_idle,
        .select_task_rq         = select_task_rq_idle,
        .set_cpus_allowed       = set_cpus_allowed_common,
 #endif

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index b3d39c3..a525447 100644 (file)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1626,7 +1626,7 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq)
        return rt_task_of(rt_se);
 }
 
-static struct task_struct *pick_next_task_rt(struct rq *rq)
+static struct task_struct *pick_task_rt(struct rq *rq)
 {
        struct task_struct *p;
 
@@ -1634,7 +1634,17 @@ static struct task_struct *pick_next_task_rt(struct rq *rq)
                return NULL;
 
        p = _pick_next_task_rt(rq);
-       set_next_task_rt(rq, p, true);
+
+       return p;
+}
+
+static struct task_struct *pick_next_task_rt(struct rq *rq)
+{
+       struct task_struct *p = pick_task_rt(rq);
+
+       if (p)
+               set_next_task_rt(rq, p, true);
+
        return p;
 }
 
@@ -2483,6 +2493,7 @@ DEFINE_SCHED_CLASS(rt) = {
 
 #ifdef CONFIG_SMP
        .balance                = balance_rt,
+       .pick_task              = pick_task_rt,
        .select_task_rq         = select_task_rq_rt,
        .set_cpus_allowed       = set_cpus_allowed_common,
        .rq_online              = rq_online_rt,

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ca30af3..fa990cd 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1953,6 +1953,9 @@ struct sched_class {
 #ifdef CONFIG_SMP
        int (*balance)(struct rq *rq, struct task_struct *prev, struct rq_flags *rf);
        int  (*select_task_rq)(struct task_struct *p, int task_cpu, int flags);
+
+       struct task_struct * (*pick_task)(struct rq *rq);
+
        void (*migrate_task_rq)(struct task_struct *p, int new_cpu);
 
        void (*task_woken)(struct rq *this_rq, struct task_struct *task);

diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
index 55f3912..f988ebe 100644 (file)
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -34,15 +34,24 @@ static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool fir
        stop->se.exec_start = rq_clock_task(rq);
 }
 
-static struct task_struct *pick_next_task_stop(struct rq *rq)
+static struct task_struct *pick_task_stop(struct rq *rq)
 {
        if (!sched_stop_runnable(rq))
                return NULL;
 
-       set_next_task_stop(rq, rq->stop, true);
        return rq->stop;
 }
 
+static struct task_struct *pick_next_task_stop(struct rq *rq)
+{
+       struct task_struct *p = pick_task_stop(rq);
+
+       if (p)
+               set_next_task_stop(rq, p, true);
+
+       return p;
+}
+
 static void
 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 {
@@ -123,6 +132,7 @@ DEFINE_SCHED_CLASS(stop) = {
 
 #ifdef CONFIG_SMP
        .balance                = balance_stop,
+       .pick_task              = pick_task_stop,
        .select_task_rq         = select_task_rq_stop,
        .set_cpus_allowed       = set_cpus_allowed_common,
 #endif