Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 8 Mar 2023 09:01:05 +0100 | Subject | Re: [PATCH v2] sched/fair: sanitize vruntime of entity being migrated |
| |
On Tue, 7 Mar 2023 at 14:41, Zhang Qiao <zhangqiao22@huawei.com> wrote: > > > > 在 2023/3/7 18:26, Vincent Guittot 写道: > > On Mon, 6 Mar 2023 at 14:53, Vincent Guittot <vincent.guittot@linaro.org> wrote: > >> > >> On Mon, 6 Mar 2023 at 13:57, Zhang Qiao <zhangqiao22@huawei.com> wrote: > >>> > >>> Commit 829c1651e9c4 ("sched/fair: sanitize vruntime of > >>> entity being placed") fix an overflowing bug, but ignore > >>> a case that se->exec_start is reset after a migration. > >>> > >>> For fixing this case, we reset the vruntime of a long > >>> sleeping task in migrate_task_rq_fair(). > >>> > >>> Fixes: 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed") > >>> Suggested-by: Vincent Guittot <vincent.guittot@linaro.org> > >>> Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com> > >> > >> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> > >> > >>> --- > >>> > >>> v1 -> v2: > >>> - fix some typos and update comments > >>> - reformat the patch > >>> > >>> --- > >>> kernel/sched/fair.c | 76 ++++++++++++++++++++++++++++++++------------- > >>> 1 file changed, 55 insertions(+), 21 deletions(-) > >>> > >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >>> index 7a1b1f855b96..74c9918ffe76 100644 > >>> --- a/kernel/sched/fair.c > >>> +++ b/kernel/sched/fair.c > >>> @@ -4648,11 +4648,45 @@ static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se) > >>> #endif > >>> } > >>> > >>> +static inline bool entity_is_long_sleep(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)) - se->exec_start; > >>> + if ((s64)sleep_time > 60LL * NSEC_PER_SEC) > >>> + return true; > >>> + > >>> + return false; > >>> +} > >>> + > >>> +static inline u64 sched_sleeper_credit(struct sched_entity *se) > >>> +{ > >>> + unsigned long thresh; > >>> + > >>> + if (se_is_idle(se)) > >>> + thresh = sysctl_sched_min_granularity; > >>> + else > >>> + thresh = sysctl_sched_latency; > >>> + > >>> + /* > >>> + * Halve their sleep time's effect, to allow > >>> + * for a gentler effect of sleepers: > >>> + */ > >>> + if (sched_feat(GENTLE_FAIR_SLEEPERS)) > >>> + thresh >>= 1; > >>> + > >>> + return thresh; > >>> +} > >>> + > >>> 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, > >>> @@ -4664,23 +4698,8 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > >>> vruntime += sched_vslice(cfs_rq, se); > >>> > >>> /* sleeps up to a single latency don't count. */ > >>> - if (!initial) { > >>> - unsigned long thresh; > >>> - > >>> - if (se_is_idle(se)) > >>> - thresh = sysctl_sched_min_granularity; > >>> - else > >>> - thresh = sysctl_sched_latency; > >>> - > >>> - /* > >>> - * Halve their sleep time's effect, to allow > >>> - * for a gentler effect of sleepers: > >>> - */ > >>> - if (sched_feat(GENTLE_FAIR_SLEEPERS)) > >>> - thresh >>= 1; > >>> - > >>> - vruntime -= thresh; > >>> - } > >>> + if (!initial) > >>> + vruntime -= sched_sleeper_credit(se); > >>> > >>> /* > >>> * Pull vruntime of the entity being placed to the base level of > >>> @@ -4689,8 +4708,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > >>> * the base as it may be too far off and the comparison may get > >>> * inversed due to s64 overflow. > >>> */ > >>> - sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; > >>> - if ((s64)sleep_time > 60LL * NSEC_PER_SEC) > >>> + if (entity_is_long_sleep(se)) > >>> se->vruntime = vruntime; > >>> else > >>> se->vruntime = max_vruntime(se->vruntime, vruntime); > >>> @@ -7635,7 +7653,23 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) > >>> if (READ_ONCE(p->__state) == TASK_WAKING) { > >>> struct cfs_rq *cfs_rq = cfs_rq_of(se); > >>> > >>> - se->vruntime -= u64_u32_load(cfs_rq->min_vruntime); > >>> + /* > >>> + * We determine whether a task sleeps for long by checking > >>> + * se->exec_start, and if it is, we sanitize its vruntime at > >>> + * place_entity(). However, after a migration, this detection > >>> + * method fails due to se->exec_start being reset. > >>> + * > >>> + * For fixing this case, we add the same check here. For a task > >>> + * which has slept for a long time, its vruntime should be reset > >>> + * to cfs_rq->min_vruntime with a sleep credit. Because waking > >>> + * task's vruntime will be added to cfs_rq->min_vruntime when > >>> + * enqueue, we only need to reset the se->vruntime of waking task > >>> + * to a credit here. > >>> + */ > >>> + if (entity_is_long_sleep(se)) > > > > I completely overlooked that we can't use rq_clock_task here. Need to > > think a bit more on this > > Hi,Vincent, > > How about using exec_start of the parent sched_entity instant of rq_clock_task()?
How do we handle sched_entity without a parent sched_entity ?
> > If during the waking sched_entity sleep, there are sibling sched_entity running, > than `pse->exec_start` was up to date. > If the cfs_rq was idle, we don't have a problem of possible overflow. > > static inline bool vruntime_need_sanitized(struct sched_entity *se) > { > struct sched_entity *pse = parent_entity(se); > u64 diff ; > > if (se->exec_start == 0 || !pse) > return false; > > diff = pse->exec_start - se->exec_start; > if ((s64)diff > 60LL * NSEC_PER_SEC) > return true; > > return false; > } > > Thanks. > ZhangQiao. > > > > >>> + se->vruntime = -sched_sleeper_credit(se); > >>> + else > >>> + se->vruntime -= u64_u32_load(cfs_rq->min_vruntime); > >>> } > >>> > >>> if (!task_on_rq_migrating(p)) { > >>> -- > >>> 2.17.1 > >>> > > . > >
| |