** Changed in: ubuntu-power-systems
Status: Triaged => In Progress
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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:
In Progress
Bug description:
== 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.
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