[PATCH v6 0/6] sched: consolidation of cpu_capacity

Vincent Guittot
2014-09-23T16:09:34Z

During load balance, the scheduler evaluates the number of tasks that a group
of CPUs can handle. The current method assumes that tasks have a fix load of
SCHED_LOAD_SCALE and CPUs have a default capacity of SCHED_CAPACITY_SCALE.
This assumption generates wrong decision by creating ghost cores or by
removing real ones when the original capacity of CPUs is different from the
default SCHED_CAPACITY_SCALE. We don't try anymore to evaluate the number of
available cores based on the group_capacity but instead we evaluate the usage
of a group and compare it with its capacity

This patchset mainly replaces the old capacity method by a new one and has kept
the policy almost unchanged whereas we could certainly take advantage of this
new statistic in several other places of the load balance.

The utilization_avg_contrib is based on the current implementation of the
load avg tracking. I also have a version of the utilization_avg_contrib that
is based on the new implementation proposal [1] but haven't provide the patches
and results as [1] is still under review. I can provide change above [1] to
change how utilization_avg_contrib is computed and adapt to new mecanism.

Change since V5
- remove patches that have been merged since v5 : patches 01, 02, 03, 04, 05, 07
- update commit log and add more details on the purpose of the patches
- fix/remove useless code with the rebase on patchset [2]
- remove capacity_orig in sched_group_capacity as it is not used
- move code in the right patch
- add some helper function to factorize code

Change since V4
- rebase to manage conflicts with changes in selection of busiest group [4]

Change since V3:
- add usage_avg_contrib statistic which sums the running time of tasks on a rq
- use usage_avg_contrib instead of runnable_avg_sum for cpu_utilization
- fix replacement power by capacity
- update some comments

Change since V2:
- rebase on top of capacity renaming
- fix wake_affine statistic update
- rework nohz_kick_needed
- optimize the active migration of a task from CPU with reduced capacity
- rename group_activity by group_utilization and remove unused total_utilization
- repair SD_PREFER_SIBLING and use it for SMT level
- reorder patchset to gather patches with same topics

Change since V1:
- add 3 fixes
- correct some commit messages
- replace capacity computation by activity
- take into account current cpu capacity

[1] https://lkml.org/lkml/2014/7/18/110
[2] https://lkml.org/lkml/2014/7/25/589

Vincent Guittot (6):
sched: add per rq cpu_capacity_orig
sched: move cfs task on a CPU with higher capacity
sched: add utilization_avg_contrib
sched: get CPU's usage statistic
sched: replace capacity_factor by usage
sched: add SD_PREFER_SIBLING for SMT level

include/linux/sched.h | 19 +++-
kernel/sched/core.c | 15 +--
kernel/sched/debug.c | 9 +-
kernel/sched/fair.c | 276 ++++++++++++++++++++++++++++++--------------------
kernel/sched/sched.h | 11 +-
5 files changed, 199 insertions(+), 131 deletions(-)

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1.9.1