[PATCH 0/7 v4] move update blocked load outside newidle_balance

[Vincent Guittot]

Joel reported long preempt and irq off sequence in newidle_balance because
of a large number of CPU cgroups in use and having to be updated. This
patchset moves the update outside newidle_imblance. This enables to early
abort during the updates in case of pending irq as an example.

Instead of kicking a normal ILB that will wakes up CPU which is already
idle, patch 6 triggers the update of statistics in the idle thread of
the CPU before selecting and entering an idle state.

Changes on v4:
- Add a dedicated bit for updating blocked load when entering idle.
  This simplifies the management of concurrency with kick_ilb.

Changes on v3:
- Fixed a compilation error for !CONFIG_SMP && CONFIG_NO_HZ_COMMON
  reported by kernel test robot <lkp@xxxxxxxxx>
- Took advantage of this new version to add a short desciption for
  nohz_run_idle_balance

Changes on v2:
- Fixed some typos and updated some comments
- Added more cleanup
- Changed to way to trigger ILB in idle thread context to remove a possible
  race condition between the normal softirq ILB and this new mecanism. The
  cpu can already be set in idle_cpus_mask because even if the cpu is added
  later when entering idle, it might not have been removed yet from previous
  idle phase.
  
Vincent Guittot (7):
  sched/fair: remove update of blocked load from newidle_balance
  sched/fair: remove unused return of _nohz_idle_balance
  sched/fair: remove unused parameter of update_nohz_stats
  sched/fair: merge for each idle cpu loop of ILB
  sched/fair: reorder newidle_balance pulled_task tests
  sched/fair: trigger the update of blocked load on newly idle cpu
  sched/fair: reduce the window for duplicated update

 kernel/sched/core.c  |   2 +-
 kernel/sched/fair.c  | 118 +++++++++++++++++--------------------------
 kernel/sched/idle.c  |   6 +++
 kernel/sched/sched.h |   7 +++
 4 files changed, 60 insertions(+), 73 deletions(-)

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2.17.1