Public bug reported: == Comment: #0 - PUVICHAKRAVARTHY RAMACHANDRAN - 2017-08-06 13:44:45 == ---Problem Description--- Significantly higher number of task migrations when the load is fixed but not balanced across cores. ---uname output--- Linux isvbos3 4.10.0-29-generic #33~16.04.1-Ubuntu SMP Tue Jul 25 18:17:06 UTC 2017 ppc64le ppc64le ppc64le GNU/Linux ---Additional Hardware Info--- Power9 dd2.0
Machine Type = Power9 ---Steps to Reproduce--- Benchmark : Multithreaded - cpu intensive. The system had 2 socket/ 32 cores/ SMT4 mode. When 64 threads was run - the migrations were less over 10s interval. when 80 threads were run - the migrations were very high. Ideally, it should have been very minimal, as the over all load was constant == Comment: #3 - SRIKAR DRONAMRAJU - 2017-08-11 06:56:47 == As suspected (commit : 05b40e0577 : "sched/fair: Prefer sibiling only if local group is under-utilized") https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=05b40e0577 should fix the problem Ran ' perf stat -a -r 5 -e sched:sched_migrate_task /home/srikar/work/ebizzy-0.3/ebizzy -t 35 -S 100' to detect the problem and verify the fix Here is perf stat without fix. Performance counter stats for 'system wide' (5 runs): 7,758 sched:sched_migrate_task ( +- 1.28% ) 100.015658079 seconds time elapsed ( +- 0.00% ) perf stat with fix. Performance counter stats for 'system wide' (5 runs): 415 sched:sched_migrate_task ( +- 11.74% ) 100.016021787 seconds time elapsed ( +- 0.00% ) git describe on upstream kernel says v4.11-rc2 # git describe 05b40e0577 v4.11-rc2-227-g05b40e0 == Comment: #4 - SRIKAR DRONAMRAJU - 2017-08-11 07:05:37 == Attaching the patch that needs to be applied to fix this bug. Verified that patch fixes the problem. ** Affects: linux (Ubuntu) Importance: Undecided Assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage) Status: New ** Tags: architecture-ppc64le bugnameltc-157336 severity-high targetmilestone-inin16043 ** Tags added: architecture-ppc64le bugnameltc-157336 severity-high targetmilestone-inin16043 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1713576 Title: More migrations with constant load To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1713576/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
