From: Vincent Guittot vincent.guittot@linaro.org
commit a53ce18cacb477dd0513c607f187d16f0fa96f71 upstream.
Commit 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed") fixes an overflowing bug, but ignore a case that se->exec_start is reset after a migration.
For fixing this case, we delay the reset of se->exec_start after placing the entity which se->exec_start to detect long sleeping task.
In order to take into account a possible divergence between the clock_task of 2 rqs, we increase the threshold to around 104 days.
Fixes: 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed") Originally-by: Zhang Qiao zhangqiao22@huawei.com Signed-off-by: Vincent Guittot vincent.guittot@linaro.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Tested-by: Zhang Qiao zhangqiao22@huawei.com Link: https://lore.kernel.org/r/20230317160810.107988-1-vincent.guittot@linaro.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/core.c | 3 ++ kernel/sched/fair.c | 53 ++++++++++++++++++++++++++++++++++++++++++---------- 2 files changed, 46 insertions(+), 10 deletions(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2082,6 +2082,9 @@ static inline void dequeue_task(struct r
void activate_task(struct rq *rq, struct task_struct *p, int flags) { + if (task_on_rq_migrating(p)) + flags |= ENQUEUE_MIGRATED; + enqueue_task(rq, p, flags);
p->on_rq = TASK_ON_RQ_QUEUED; --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4636,11 +4636,33 @@ static void check_spread(struct cfs_rq * #endif }
+static inline bool entity_is_long_sleeper(struct sched_entity *se) +{ + struct cfs_rq *cfs_rq; + u64 sleep_time; + + if (se->exec_start == 0) + return false; + + cfs_rq = cfs_rq_of(se); + + sleep_time = rq_clock_task(rq_of(cfs_rq)); + + /* Happen while migrating because of clock task divergence */ + if (sleep_time <= se->exec_start) + return false; + + sleep_time -= se->exec_start; + if (sleep_time > ((1ULL << 63) / scale_load_down(NICE_0_LOAD))) + return true; + + return false; +} + static void place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) { u64 vruntime = cfs_rq->min_vruntime; - u64 sleep_time;
/* * The 'current' period is already promised to the current tasks, @@ -4672,13 +4694,24 @@ place_entity(struct cfs_rq *cfs_rq, stru
/* * Pull vruntime of the entity being placed to the base level of - * cfs_rq, to prevent boosting it if placed backwards. If the entity - * slept for a long time, don't even try to compare its vruntime with - * the base as it may be too far off and the comparison may get - * inversed due to s64 overflow. + * cfs_rq, to prevent boosting it if placed backwards. + * However, min_vruntime can advance much faster than real time, with + * the extreme being when an entity with the minimal weight always runs + * on the cfs_rq. If the waking entity slept for a long time, its + * vruntime difference from min_vruntime may overflow s64 and their + * comparison may get inversed, so ignore the entity's original + * vruntime in that case. + * The maximal vruntime speedup is given by the ratio of normal to + * minimal weight: scale_load_down(NICE_0_LOAD) / MIN_SHARES. + * When placing a migrated waking entity, its exec_start has been set + * from a different rq. In order to take into account a possible + * divergence between new and prev rq's clocks task because of irq and + * stolen time, we take an additional margin. + * So, cutting off on the sleep time of + * 2^63 / scale_load_down(NICE_0_LOAD) ~ 104 days + * should be safe. */ - sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; - if ((s64)sleep_time > 60LL * NSEC_PER_SEC) + if (entity_is_long_sleeper(se)) se->vruntime = vruntime; else se->vruntime = max_vruntime(se->vruntime, vruntime); @@ -4758,6 +4791,9 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
if (flags & ENQUEUE_WAKEUP) place_entity(cfs_rq, se, 0); + /* Entity has migrated, no longer consider this task hot */ + if (flags & ENQUEUE_MIGRATED) + se->exec_start = 0;
check_schedstat_required(); update_stats_enqueue_fair(cfs_rq, se, flags); @@ -7460,9 +7496,6 @@ static void migrate_task_rq_fair(struct /* Tell new CPU we are migrated */ se->avg.last_update_time = 0;
- /* We have migrated, no longer consider this task hot */ - se->exec_start = 0; - update_scan_period(p, new_cpu); }