Messages in this thread | | | From | Dawei Li <> | Date | Mon, 1 Apr 2024 22:47:36 -0700 | Subject | Re: [PATCH v2] sched/fair: fix initial util_avg calculation |
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Hi Vishal
Thanks for the comment! Do you suggest using scale_load_down() in place of se_weight()? It's a soft bug we should fix one way or another before what the comment mentions really happens. I am actually confused that we have both se_weight() and scale_load_down(), and they do the same thing.
Best regards, Dawei
On Mon, Apr 1, 2024 at 3:36 AM Vishal Chourasia <vishalc@linux.ibm.com> wrote: > > 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->loadweight; > > + 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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