Messages in this thread |  | | Date | Sat, 28 Jan 2023 18:41:33 +0800 | Subject | Re: [PATCH] sched/fair: sanitize vruntime of entity being placed | From | Zhang Qiao <> |
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在 2023/1/28 0:32, Roman Kagan 写道: > From: Zhang Qiao <zhangqiao22@huawei.com> > > When a scheduling entity is placed onto cfs_rq, its vruntime is pulled > to the base level (around cfs_rq->min_vruntime), so that the entity > doesn't gain extra boost when placed backwards. > > However, if the entity being placed wasn't executed for a long time, its > vruntime may get too far behind (e.g. while cfs_rq was executing a > low-weight hog), which can inverse the vruntime comparison due to s64 > overflow. This results in the entity being placed with its original > vruntime way forwards, so that it will effectively never get to the cpu. > > To prevent that, ignore the vruntime of the entity being placed if it > didn't execute for much longer than the characteristic sheduler time > scale. >
Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
> [rkagan: formatted, adjusted commit log, comments, cutoff value] > Co-developed-by: Roman Kagan <rkagan@amazon.de> > Signed-off-by: Roman Kagan <rkagan@amazon.de> > --- > @zhangqiao22, I took the liberty to put you as the author of the patch, > as this is essentially what you posted for discussion, with minor > tweaks. Please stamp with your s-o-b if you're ok with it. > > kernel/sched/fair.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 0f8736991427..d6cf131ebb0b 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4656,6 +4656,7 @@ 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, > @@ -4685,8 +4686,18 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > vruntime -= thresh; > } > > - /* ensure we never gain time by being placed backwards. */ > - se->vruntime = max_vruntime(se->vruntime, vruntime); > + /* > + * 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. > + */ > + sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; > + if ((s64)sleep_time > 60 * NSEC_PER_SEC)
In order to avoid overflowing, it'd better be "60LL * NSEC_PER_SEC"
Thanks, Qiao.
> + se->vruntime = vruntime; > + else > + se->vruntime = max_vruntime(se->vruntime, vruntime); > } > > static void check_enqueue_throttle(struct cfs_rq *cfs_rq); >
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