From: Peter Zijlstra <pet...@infradead.org>
Use deadline servers to service fair tasks.
This patch adds a fair_server deadline entity which acts as a container
for fair entities and can be used to fix starvation when higher priority
(wrt fair) tasks are monopolizing CPU(s).
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
kernel/sched/core.c | 1 +
kernel/sched/fair.c | 29 +++++++++++++++++++++++++++++
kernel/sched/sched.h | 4 ++++
3 files changed, 34 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7c471961fd0b8..6537637139c63 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7170,6 +7170,7 @@ void __init sched_init(void)
#endif /* CONFIG_SMP */
hrtick_rq_init(rq);
atomic_set(&rq->nr_iowait, 0);
+ fair_server_init(rq);
}
set_load_weight(&init_task, false);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5130239c0e1e5..6a97ee2a4e26d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5514,6 +5514,9 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p,
int flags)
*/
util_est_enqueue(&rq->cfs, p);
+ if (!rq->cfs.h_nr_running)
+ dl_server_start(&rq->fair_server);
+
/*
* If in_iowait is set, the code below may not trigger any cpufreq
* utilization updates, so do it here explicitly with the IOWAIT flag
@@ -5666,6 +5669,9 @@ static void dequeue_task_fair(struct rq *rq, struct
task_struct *p, int flags)
rq->next_balance = jiffies;
dequeue_throttle:
+ if (!rq->cfs.h_nr_running)
+ dl_server_stop(&rq->fair_server);
+
util_est_dequeue(&rq->cfs, p, task_sleep);
hrtick_update(rq);
}
@@ -7151,6 +7157,29 @@ static struct task_struct *__pick_next_task_fair(struct
rq *rq)
return pick_next_task_fair(rq, NULL, NULL);
}
+static bool fair_server_has_tasks(struct sched_dl_entity *dl_se)
+{
+ return !!dl_se->rq->cfs.nr_running;
+}
+
+static struct task_struct *fair_server_pick(struct sched_dl_entity *dl_se)
+{
+ return pick_next_task_fair(dl_se->rq, NULL, NULL);
+}
+
+void fair_server_init(struct rq *rq)
+{
+ struct sched_dl_entity *dl_se = &rq->fair_server;
+
+ init_dl_entity(dl_se);
+
+ dl_se->dl_runtime = TICK_NSEC;
+ dl_se->dl_deadline = 20 * TICK_NSEC;
+ dl_se->dl_period = 20 * TICK_NSEC;
+
+ dl_server_init(dl_se, rq, fair_server_has_tasks, fair_server_pick);
+}
+
/*
* Account for a descheduled task:
*/
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f035cd8ccd224..bf8c9c07705c9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -375,6 +375,8 @@ extern void dl_server_init(struct sched_dl_entity *dl_se,
struct rq *rq,
dl_server_has_tasks_f has_tasks,
dl_server_pick_f pick);
+extern void fair_server_init(struct rq *);
+
#ifdef CONFIG_CGROUP_SCHED
#include <linux/cgroup.h>
@@ -959,6 +961,8 @@ struct rq {
struct rt_rq rt;
struct dl_rq dl;
+ struct sched_dl_entity fair_server;
+
#ifdef CONFIG_FAIR_GROUP_SCHED
/* list of leaf cfs_rq on this CPU: */
struct list_head leaf_cfs_rq_list;
--
2.26.2
