Messages in this thread Patch in this message | | | From | Daniel Bristot de Oliveira <> | Subject | [PATCH v5 5/7] sched/fair: Add trivial fair server | Date | Sat, 4 Nov 2023 11:59:22 +0100 |
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From: Peter Zijlstra <peterz@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).
[ dl_server do not account for rt ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org> --- kernel/sched/core.c | 1 + kernel/sched/deadline.c | 7 +++++++ kernel/sched/fair.c | 29 +++++++++++++++++++++++++++++ kernel/sched/sched.h | 4 ++++ 4 files changed, 41 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a721f6776b12..939266d29681 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -10019,6 +10019,7 @@ void __init sched_init(void) #endif /* CONFIG_SMP */ hrtick_rq_init(rq); atomic_set(&rq->nr_iowait, 0); + fair_server_init(rq); #ifdef CONFIG_SCHED_CORE rq->core = rq; diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 541d547e1019..1d7b96ca9011 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1382,6 +1382,13 @@ static void update_curr_dl_se(struct rq *rq, struct sched_dl_entity *dl_se, s64 resched_curr(rq); } + /* + * The fair server (sole dl_server) does not account for real-time + * workload because it is running fair work. + */ + if (dl_server(dl_se)) + return; + /* * Because -- for now -- we share the rt bandwidth, we need to * account our runtime there too, otherwise actual rt tasks diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bc3a4bc6c438..b15f7f376a67 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6600,6 +6600,9 @@ 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 @@ -6744,6 +6747,9 @@ 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_update(&rq->cfs, p, task_sleep); hrtick_update(rq); } @@ -8396,6 +8402,29 @@ 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 = 50 * NSEC_PER_MSEC; + dl_se->dl_deadline = 1000 * NSEC_PER_MSEC; + dl_se->dl_period = 1000 * NSEC_PER_MSEC; + + 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 24a2bc7c453b..ec0e288c8e06 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -340,6 +340,8 @@ 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 struct cfs_rq; @@ -1005,6 +1007,8 @@ 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; -- 2.40.1
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