** Description changed: + == SRU Justification == + There is a significantly higher number of task migrations when the load is + fixed and not balanced across cores. + + Benchmark results are posted in the bug description and in the commits + git log. + + This bug is resolved by mainline commit 05b40e057734811ce452344fb3690d09965a7b6a, which is + in mailine as of 4.12-rc1. + + + == Fix == + commit 05b40e057734811ce452344fb3690d09965a7b6a + Author: Srikar Dronamraju <[email protected]> + Date: Wed Mar 22 23:27:50 2017 +0530 + + sched/fair: Prefer sibiling only if local group is under-utilized + + == Regression Potential == + Medium, since this commit does touch the scheduler. However, the commit only makes a change to + allow a local group to pull a task, if the source group has more number of + tasks than the local group. + + == Test Case == + A test kernel was built with this patch and tested by the original bug reporter. + The bug reporter states the test kernel resolved the bug. + + + == 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 + Power9 dd2.0 - Machine Type = Power9 - + Machine Type = Power9 + ---Steps to Reproduce--- - Benchmark : Multithreaded - cpu intensive. The system had 2 socket/ 32 cores/ SMT4 mode. + 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 - + 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 + 7,758 sched:sched_migrate_task ( +- 1.28% ) - 100.015658079 seconds time elapsed + 100.015658079 seconds time elapsed ( +- 0.00% ) perf stat with fix. Performance counter stats for 'system wide' (5 runs): - 415 sched:sched_migrate_task + 415 sched:sched_migrate_task ( +- 11.74% ) - 100.016021787 seconds time elapsed + 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.
-- 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-power-systems/+bug/1713576/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
