Messages in this thread | | | Date | Tue, 7 Mar 2023 22:06:37 +0800 | Subject | Re: [PATCH v2] sched/fair: sanitize vruntime of entity being migrated | From | Zhang Qiao <> |
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在 2023/3/7 20:45, Dietmar Eggemann 写道: > On 06/03/2023 14:24, Zhang Qiao 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> > > [...] > >> @@ -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 > > Isn't this the other way around? `vruntime += min_vruntime` > >> + * enqueue, we only need to reset the se->vruntime of waking task >> + * to a credit here. > > You not reset it to credit, you subtract the credit from vruntime ? > > I assume this is done to have sleeper credit accounted on both > (se->vruntime and vruntime) for `se->vruntime = > max_vruntime(se->vruntime, vruntime)` in place_entity() since > entity_is_long_sleep(se)=false for a remove wakeup since `se->exec_start=0`. > > >> + */ >> + if (entity_is_long_sleep(se)) >> + se->vruntime = -sched_sleeper_credit(se); >> + else >> + se->vruntime -= u64_u32_load(cfs_rq->min_vruntime); > > Not sure I understand this part. > Don't we have to do `vruntime -= min_vruntime` here for long sleeping > task as well?
Hi, Dietmar,
At this time, `se->vruntime - min_vruntime` maybe greater than s64max as well.
thanks, ZhangQiao
> > Since we always do the `vruntime += min_vruntime` on the new CPU for a > remote wakeup. > > [...] > > . >
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