[PATCH v7 0/7] sched: consolidation of cpu_capacity

[Vincent Guittot]

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 V6
 - add group usage tracking
 - fix some commits' messages
 - minor fix like comments and argument order

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

Morten Rasmussen (1):
  sched: Track group sched_entity usage contributions

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 |  21 +++-
 kernel/sched/core.c   |  15 +--
 kernel/sched/debug.c  |  12 ++-
 kernel/sched/fair.c   | 283 ++++++++++++++++++++++++++++++--------------------
 kernel/sched/sched.h  |  11 +-
 5 files changed, 209 insertions(+), 133 deletions(-)

-- 
1.9.1

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