Later commits will change CFS bandwidth control throttling from a per-cfs_rq basis to a per-task basis. This means special care needs to be taken around any transition a task can have into and out of a cfs_rq.
To ease reviewing, the transitions are patched with dummy-helpers that are implemented later on. Add helpers to migrate_task_rq_fair() to cover CPU migration. Even if the task stays within the same taskgroup, each cfs_rq has its own runtime accounting, thus the task needs to be throttled or unthrottled accordingly. Signed-off-by: Valentin Schneider <[email protected]> --- kernel/sched/fair.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ec4cf7308a586..b2242307677ca 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5694,8 +5694,11 @@ static inline int throttled_hierarchy(struct cfs_rq *cfs_rq) return cfs_bandwidth_used() && cfs_rq->throttle_count; } +static inline bool task_has_throttle_work(struct task_struct *p) { return false; } static inline bool task_needs_throttling(struct task_struct *p) { return false; } +static inline bool task_needs_migrate_throttling(struct task_struct *p, unsigned int dst_cpu) { return false; } static inline void task_throttle_setup(struct task_struct *p) { } +static inline void task_throttle_cancel_migrate(struct task_struct *p, int dst_cpu) { } static inline void task_throttle_cancel(struct task_struct *p) { } /* @@ -6626,8 +6629,11 @@ static inline int throttled_lb_pair(struct task_group *tg, return 0; } +static inline bool task_has_throttle_work(struct task_struct *p) { return false; } static inline bool task_needs_throttling(struct task_struct *p) { return false; } +static inline bool task_needs_migrate_throttling(struct task_struct *p, unsigned int dst_cpu) { return false; } static inline void task_throttle_setup(struct task_struct *p) { } +static inline void task_throttle_cancel_migrate(struct task_struct *p, int dst_cpu) { } static inline void task_throttle_cancel(struct task_struct *p) { } #ifdef CONFIG_FAIR_GROUP_SCHED @@ -8308,6 +8314,24 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) se->avg.last_update_time = 0; update_scan_period(p, new_cpu); + + if (!cfs_bandwidth_used()) + return; + /* + * When the runtime within a cfs_bandwidth is depleted, all underlying + * cfs_rq's can have (approximately) sched_cfs_bandwidth_slice() runtime + * remaining. + * + * This means all tg->cfs_rq[]'s do not get throttled at the exact same + * time: some may still have a bit of runtime left. Thus, even if the + * task is staying within the same cgroup, and under the same + * cfs_bandwidth, the cfs_rq it migrates to might have a different + * throttle status - resync is needed. + */ + if (task_needs_migrate_throttling(p, new_cpu)) + task_throttle_setup(p); + else if (task_has_throttle_work(p)) + task_throttle_cancel_migrate(p, new_cpu); } static void task_dead_fair(struct task_struct *p) -- 2.43.0
