Messages in this thread Patch in this message | | | From | Vineeth Remanan Pillai <> | Subject | [RFC PATCH 07/16] sched/fair: Fix forced idle sibling starvation corner case | Date | Tue, 30 Jun 2020 21:32:28 +0000 |
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From: vpillai <vpillai@digitalocean.com>
If there is only one long running local task and the sibling is forced idle, it might not get a chance to run until a schedule event happens on any cpu in the core.
So we check for this condition during a tick to see if a sibling is starved and then give it a chance to schedule.
Signed-off-by: Vineeth Remanan Pillai <vpillai@digitalocean.com> Signed-off-by: Julien Desfossez <jdesfossez@digitalocean.com> --- kernel/sched/fair.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ae17507533a0..49fb93296e35 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10613,6 +10613,40 @@ static void rq_offline_fair(struct rq *rq) #endif /* CONFIG_SMP */ +#ifdef CONFIG_SCHED_CORE +static inline bool +__entity_slice_used(struct sched_entity *se) +{ + return (se->sum_exec_runtime - se->prev_sum_exec_runtime) > + sched_slice(cfs_rq_of(se), se); +} + +/* + * If runqueue has only one task which used up its slice and if the sibling + * is forced idle, then trigger schedule to give forced idle task a chance. + */ +static void resched_forceidle_sibling(struct rq *rq, struct sched_entity *se) +{ + int cpu = cpu_of(rq), sibling_cpu; + + if (rq->cfs.nr_running > 1 || !__entity_slice_used(se)) + return; + + for_each_cpu(sibling_cpu, cpu_smt_mask(cpu)) { + struct rq *sibling_rq; + if (sibling_cpu == cpu) + continue; + if (cpu_is_offline(sibling_cpu)) + continue; + + sibling_rq = cpu_rq(sibling_cpu); + if (sibling_rq->core_forceidle) { + resched_curr(sibling_rq); + } + } +} +#endif + /* * scheduler tick hitting a task of our scheduling class. * @@ -10636,6 +10670,11 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) update_misfit_status(curr, rq); update_overutilized_status(task_rq(curr)); + +#ifdef CONFIG_SCHED_CORE + if (sched_core_enabled(rq)) + resched_forceidle_sibling(rq, &curr->se); +#endif } /* -- 2.17.1
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