linux/kernel/sched
kuyo chang 40f5aa4c5e sched/pelt: Fix attach_entity_load_avg() corner case
The warning in cfs_rq_is_decayed() triggered:

    SCHED_WARN_ON(cfs_rq->avg.load_avg ||
		  cfs_rq->avg.util_avg ||
		  cfs_rq->avg.runnable_avg)

There exists a corner case in attach_entity_load_avg() which will
cause load_sum to be zero while load_avg will not be.

Consider se_weight is 88761 as per the sched_prio_to_weight[] table.
Further assume the get_pelt_divider() is 47742, this gives:
se->avg.load_avg is 1.

However, calculating load_sum:

  se->avg.load_sum = div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se));
  se->avg.load_sum = 1*47742/88761 = 0.

Then enqueue_load_avg() adds this to the cfs_rq totals:

  cfs_rq->avg.load_avg += se->avg.load_avg;
  cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;

Resulting in load_avg being 1 with load_sum is 0, which will trigger
the WARN.

Fixes: f207934fb7 ("sched/fair: Align PELT windows between cfs_rq and its se")
Signed-off-by: kuyo chang <kuyo.chang@mediatek.com>
[peterz: massage changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lkml.kernel.org/r/20220414090229.342-1-kuyo.chang@mediatek.com
2022-04-19 21:15:41 +02:00
..
Makefile
autogroup.c
autogroup.h
build_policy.c
build_utility.c
clock.c
completion.c
core.c sched: Teach the forced-newidle balancer about CPU affinity limitation. 2022-04-05 09:59:36 +02:00
core_sched.c
cpuacct.c
cpudeadline.c
cpudeadline.h
cpufreq.c
cpufreq_schedutil.c Changes in this cycle were: 2022-03-22 14:39:12 -07:00
cpupri.c
cpupri.h
cputime.c
deadline.c
debug.c
fair.c sched/pelt: Fix attach_entity_load_avg() corner case 2022-04-19 21:15:41 +02:00
features.h
idle.c sched/core: Fix forceidle balancing 2022-04-05 09:59:36 +02:00
isolation.c
loadavg.c
membarrier.c
pelt.c
pelt.h
psi.c
rt.c
sched-pelt.h
sched.h sched/core: Fix forceidle balancing 2022-04-05 09:59:36 +02:00
smp.h
stats.c
stats.h
stop_task.c
swait.c
topology.c
wait.c
wait_bit.c