This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed- zesty' to 'verification-done-zesty'. If the problem still exists, change the tag 'verification-needed-zesty' to 'verification-failed-zesty'.
If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you! ** Tags added: verification-needed-zesty -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1713576 Title: More migrations with constant load Status in The Ubuntu-power-systems project: In Progress Status in linux package in Ubuntu: In Progress Status in linux source package in Zesty: Fix Committed Bug description: == 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 <sri...@linux.vnet.ibm.com> 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 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. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-power-systems/+bug/1713576/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
