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    Subject[PATCH v3 0/8] sched/fair: rework the CFS load balance
    Date
    Several wrong task placement have been raised with the current load
    balance algorithm but their fixes are not always straight forward and
    end up with using biased values to force migrations. A cleanup and rework
    of the load balance will help to handle such UCs and enable to fine grain
    the behavior of the scheduler for other cases.

    Patch 1 has already been sent separately and only consolidate asym policy
    in one place and help the review of the changes in load_balance.

    Patch 2 renames the sum of h_nr_running in stats.

    Patch 3 removes meaningless imbalance computation to make review of
    patch 4 easier.

    Patch 4 reworks load_balance algorithm and fixes some wrong task placement
    but try to stay conservative.

    Patch 5 add the sum of nr_running to monitor non cfs tasks and take that
    into account when pulling tasks.

    Patch 6 replaces runnable_load by load now that the signal is only used
    when overloaded.

    Patch 7 improves the spread of tasks at the 1st scheduling level.

    Patch 8 uses utilization instead of load in all steps of misfit task
    path.

    Patch 9 replaces runnable_load_avg by load_avg in the wake up path.

    Patch 10 optimizes find_idlest_group() that was using both runnable_load
    and load. This has not been squashed with previous patch to ease the
    review.

    Some benchmarks results based on 8 iterations of each tests:
    - small arm64 dual quad cores system

    tip/sched/core w/ this patchset improvement
    schedpipe 54981 +/-0.36% 55459 +/-0.31% (+0.97%)

    hackbench
    1 groups 0.906 +/-2.34% 0.906 +/-2.88% (+0.06%)

    - large arm64 2 nodes / 224 cores system

    tip/sched/core w/ this patchset improvement
    schedpipe 125323 +/-0.98% 125624 +/-0.71% (+0.24%)

    hackbench -l (256000/#grp) -g #grp
    1 groups 15.360 +/-1.76% 14.206 +/-1.40% (+8.69%)
    4 groups 5.822 +/-1.02% 5.508 +/-6.45% (+5.38%)
    16 groups 3.103 +/-0.80% 3.244 +/-0.77% (-4.52%)
    32 groups 2.892 +/-1.23% 2.850 +/-1.81% (+1.47%)
    64 groups 2.825 +/-1.51% 2.725 +/-1.51% (+3.54%)
    128 groups 3.149 +/-8.46% 3.053 +/-13.15% (+3.06%)
    256 groups 3.511 +/-8.49% 3.019 +/-1.71% (+14.03%)

    dbench
    1 groups 329.677 +/-0.46% 329.771 +/-0.11% (+0.03%)
    4 groups 931.499 +/-0.79% 947.118 +/-0.94% (+1.68%)
    16 groups 1924.210 +/-0.89% 1947.849 +/-0.76% (+1.23%)
    32 groups 2350.646 +/-5.75% 2351.549 +/-6.33% (+0.04%)
    64 groups 2201.524 +/-3.35% 2192.749 +/-5.84% (-0.40%)
    128 groups 2206.858 +/-2.50% 2376.265 +/-7.44% (+7.68%)
    256 groups 1263.520 +/-3.34% 1633.143 +/-13.02% (+29.25%)

    tip/sched/core sha1:
    0413d7f33e60 ('sched/uclamp: Always use 'enum uclamp_id' for clamp_id values')

    Changes since v2:
    - fix typo and reorder code
    - some minor code fixes
    - optimize the find_idles_group()

    Not covered in this patchset:
    - update find_idlest_group() to be more aligned with load_balance(). I didn't
    want to delay this version because of this update which is not ready yet
    - Better detection of overloaded and fully busy state, especially for cases
    when nr_running > nr CPUs.

    Vincent Guittot (8):
    sched/fair: clean up asym packing
    sched/fair: rename sum_nr_running to sum_h_nr_running
    sched/fair: remove meaningless imbalance calculation
    sched/fair: rework load_balance
    sched/fair: use rq->nr_running when balancing load
    sched/fair: use load instead of runnable load in load_balance
    sched/fair: evenly spread tasks when not overloaded
    sched/fair: use utilization to select misfit task
    sched/fair: use load instead of runnable load in wakeup path
    sched/fair: optimize find_idlest_group

    kernel/sched/fair.c | 805 +++++++++++++++++++++++++++-------------------------
    1 file changed, 417 insertions(+), 388 deletions(-)

    --
    2.7.4

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