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sched/fair: Sanitize vruntime of entity being migrated

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Commit 829c1651e9 ("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: 829c1651e9 ("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
This commit is contained in:
Vincent Guittot 2023-03-17 17:08:10 +01:00 committed by Peter Zijlstra
parent e8d018dd02
commit a53ce18cac
2 changed files with 46 additions and 10 deletions
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3
kernel/sched/core.c
View File

@ -2084,6 +2084,9 @@ static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
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;

53
kernel/sched/fair.c
View File

@ -4648,11 +4648,33 @@ static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se)
#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,
@ -4684,13 +4706,24 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
/*
* 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);
@ -4770,6 +4803,9 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
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);
@ -7657,9 +7693,6 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu)
/* 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);
}