[PATCH v6 0/9] sched/fair: task load tracking optimization and cleanup

[Chengming Zhou]

Hi all,

This patch series is optimization and cleanup for task load tracking when
task migrate CPU/cgroup or switched_from/to_fair(), based on tip/sched/core.

There are three types of detach/attach_entity_load_avg (except fork and exit)
for a fair task:
1. task migrate CPU (on_rq migrate or wake_up migrate)
2. task migrate cgroup (detach and attach)
3. task switched_from/to_fair (detach later attach)

patch 1-3 cleanup the task change cgroup case by remove cpu_cgrp_subsys->fork(),
since we already do the same thing in sched_cgroup_fork().

patch 5/9 optimize the task migrate CPU case by combine detach into dequeue.

patch 6/9 fix another detach on unattached task case which has been woken up
by try_to_wake_up() but is waiting for actually being woken up by
sched_ttwu_pending().

patch 7/9 remove unnecessary limitation that we would fail when change
cgroup of forked task which hasn't been woken up by wake_up_new_task().

patch 8-9 optimize post_init_entity_util_avg() for fair task and skip
setting util_avg and runnable_avg for !fair task at the fork time.

Thanks!


Changes in v6:
 - Use TASK_NEW to check new forked task which hasn't been woken up
   by wake_up_new_task(), suggested by Peter Zijlstra. Thanks!
 - Update comments related to post_init_entity_util_avg() in patch 8/9.

Changes in v5:
 - Don't do code movements in patch 6/9, which complicate code review,
   as suggested by Vincent. Thanks!
 - Fix a build error of typo in patch 7/9.

Changes in v4:
 - Drop detach/attach_entity_cfs_rq() refactor patch in the last version.
 - Move new forked task check to task_change_group_fair().

Changes in v3:
 - One big change is this series don't freeze PELT sum/avg values to be
   used as initial values when re-entering fair any more, since these
   PELT values become much less relevant.
 - Reorder patches and collect tags from Vincent and Dietmar. Thanks!
 - Fix detach on unattached task which has been woken up by try_to_wake_up()
   but is waiting for actually being woken up by sched_ttwu_pending().
 - Delete TASK_NEW which limit forked task from changing cgroup.
 - Don't init util_avg and runnable_avg for !fair taks at fork time.

Changes in v2:
 - split task se depth maintenance into a separate patch3, suggested
   by Peter.
 - reorder patch6-7 before patch8-9, since we need update_load_avg()
   to do conditional attach/detach to avoid corner cases like twice
   attach problem.

Chengming Zhou (9):
  sched/fair: maintain task se depth in set_task_rq()
  sched/fair: remove redundant cpu_cgrp_subsys->fork()
  sched/fair: reset sched_avg last_update_time before set_task_rq()
  sched/fair: update comments in enqueue/dequeue_entity()
  sched/fair: combine detach into dequeue when migrating task
  sched/fair: fix another detach on unattached task corner case
  sched/fair: allow changing cgroup of new forked task
  sched/fair: move task sched_avg attach to enqueue_task_fair()
  sched/fair: don't init util/runnable_avg for !fair task

 kernel/sched/core.c  |  52 ++++---------------
 kernel/sched/fair.c  | 120 ++++++++++++++++++++-----------------------
 kernel/sched/sched.h |   6 +--
 3 files changed, 66 insertions(+), 112 deletions(-)

-- 
2.37.2