Messages in this thread | | | Date | Mon, 1 Apr 2024 16:06:00 +0530 | From | Vishal Chourasia <> | Subject | Re: [PATCH v2] sched/fair: fix initial util_avg calculation |
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On Thu, Mar 14, 2024 at 06:59:16PM -0700, Dawei Li wrote: > Change se->load.weight to se_weight(se) in the calculation for the > initial util_avg to avoid unnecessarily inflating the util_avg by 1024 > times. > > The reason is that se->load.weight has the unit/scale as the scaled-up > load, while cfs_rg->avg.load_avg has the unit/scale as the true task > weight (as mapped directly from the task's nice/priority value). With > CONFIG_32BIT, the scaled-up load is equal to the true task weight. With > CONFIG_64BIT, the scaled-up load is 1024 times the true task weight. > Thus, the current code may inflate the util_avg by 1024 times. The > follow-up capping will not allow the util_avg value to go wild. But the > calculation should have the correct logic. > > Signed-off-by: Dawei Li <daweilics@gmail.com> > --- > Changes in v2: > - update the commit message > --- > kernel/sched/fair.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index a19ea290b790..5f98f639bdb9 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1031,7 +1031,8 @@ void init_entity_runnable_average(struct sched_entity *se) > * With new tasks being created, their initial util_avgs are extrapolated > * based on the cfs_rq's current util_avg: > * > - * util_avg = cfs_rq->util_avg / (cfs_rq->load_avg + 1) * se.load.weight > + * util_avg = cfs_rq->avg.util_avg / (cfs_rq->avg.load_avg + 1) > + * * se_weight(se) > * > * However, in many cases, the above util_avg does not give a desired > * value. Moreover, the sum of the util_avgs may be divergent, such > @@ -1078,7 +1079,7 @@ void post_init_entity_util_avg(struct task_struct *p) > > if (cap > 0) { > if (cfs_rq->avg.util_avg != 0) { > - sa->util_avg = cfs_rq->avg.util_avg * se->load.weight; > + sa->util_avg = cfs_rq->avg.util_avg * se_weight(se); Hi,
The comment above the declaration of se_weight function says we should be using full load resolution and get rid of this helper.
Should we be adding new user of the helper?
/* * XXX we want to get rid of these helpers and use the full load resolution. */ static inline long se_weight(struct sched_entity *se) { return scale_load_down(se->load.weight); }
> sa->util_avg /= (cfs_rq->avg.load_avg + 1); > > if (sa->util_avg > cap) > -- > 2.40.1 >
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