Re: [PATCH 1/2] sched/fair: pelt: use u32 for util_avg

kbuild test robot
2018-06-05T01:34:22Z

[-- Attachment #1: Type: text/plain, Size: 3283 bytes --]

Hi Patrick,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on tip/sched/core]
[also build test ERROR on v4.17 next-20180604]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Patrick-Bellasi/sched-fair-pelt-use-u32-for-util_avg/20180605-082640
config: i386-randconfig-s0-201822 (attached as .config)
compiler: gcc-6 (Debian 6.4.0-9) 6.4.0 20171026
reproduce:
# save the attached .config to linux build tree
make ARCH=i386

All errors (new ones prefixed by >>):

kernel/sched/fair.o: In function `post_init_entity_util_avg':
>> kernel/sched/fair.c:761: undefined reference to `__udivdi3'

vim +761 kernel/sched/fair.c

724
725 /*
726 * With new tasks being created, their initial util_avgs are extrapolated
727 * based on the cfs_rq's current util_avg:
728 *
729 * util_avg = cfs_rq->util_avg / (cfs_rq->load_avg + 1) * se.load.weight
730 *
731 * However, in many cases, the above util_avg does not give a desired
732 * value. Moreover, the sum of the util_avgs may be divergent, such
733 * as when the series is a harmonic series.
734 *
735 * To solve this problem, we also cap the util_avg of successive tasks to
736 * only 1/2 of the left utilization budget:
737 *
738 * util_avg_cap = (1024 - cfs_rq->avg.util_avg) / 2^n
739 *
740 * where n denotes the nth task.
741 *
742 * For example, a simplest series from the beginning would be like:
743 *
744 * task util_avg: 512, 256, 128, 64, 32, 16, 8, ...
745 * cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ...
746 *
747 * Finally, that extrapolated util_avg is clamped to the cap (util_avg_cap)
748 * if util_avg > util_avg_cap.
749 */
750 void post_init_entity_util_avg(struct sched_entity *se)
751 {
752 struct cfs_rq *cfs_rq = cfs_rq_of(se);
753 long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2;
754
755 if (cap > 0) {
756 struct sched_avg *sa = &se->avg;
757 u64 util_avg = READ_ONCE(sa->util_avg);
758
759 if (cfs_rq->avg.util_avg != 0) {
760 util_avg = cfs_rq->avg.util_avg * se->load.weight;
> 761 util_avg /= (cfs_rq->avg.load_avg + 1);
762 if (util_avg > cap)
763 util_avg = cap;
764 } else {
765 util_avg = cap;
766 }
767
768 WRITE_ONCE(sa->util_avg, util_avg);
769 }
770
771 if (entity_is_task(se)) {
772 struct task_struct *p = task_of(se);
773 if (p->sched_class != &fair_sched_class) {
774 /*
775 * For !fair tasks do:
776 *
777 update_cfs_rq_load_avg(now, cfs_rq);
778 attach_entity_load_avg(cfs_rq, se, 0);
779 switched_from_fair(rq, p);
780 *
781 * such that the next switched_to_fair() has the
782 * expected state.
783 */
784 se->avg.last_update_time = cfs_rq_clock_task(cfs_rq);
785 return;
786 }
787 }
788
789 attach_entity_cfs_rq(se);
790 }
791

---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 28035 bytes --]