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Subject[PATCH v2 0/5] remove runnable_load_avg and improve group_classify
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This new version stays quite close to the previous one and should 
replace without problems the previous one that part of Mel's patchset:
https://lkml.org/lkml/2020/2/14/156

NUMA load balancing is the last remaining piece of code that uses the
runnable_load_avg of PELT to balance tasks between nodes. The normal
load_balance has replaced it by a better description of the current state
of the group of cpus. The same policy can be applied to the numa
balancing.

Once unused, runnable_load_avg can be replaced by a simpler runnable_avg
signal that tracks the waiting time of tasks on rq. Currently, the state
of a group of CPUs is defined thanks to the number of running task and the
level of utilization of rq. But the utilization can be temporarly low
after the migration of a task whereas the rq is still overloaded with
tasks. In such case where tasks were competing for the rq, the
runnable_avg will stay high after the migration.

Some hackbench results:

- small arm64 dual quad cores system
hackbench -l (2560/#grp) -g #grp

grp tip/sched/core +patchset improvement
1 1,327(+/-10,06 %) 1,247(+/-5,45 %) 5,97 %
4 1,250(+/- 2,55 %) 1,207(+/-2,12 %) 3,42 %
8 1,189(+/- 1,47 %) 1,179(+/-1,93 %) 0,90 %
16 1,221(+/- 3,25 %) 1,219(+/-2,44 %) 0,16 %

- large arm64 2 nodes / 224 cores system
hackbench -l (256000/#grp) -g #grp

grp tip/sched/core +patchset improvement
1 14,197(+/- 2,73 %) 13,917(+/- 2,19 %) 1,98 %
4 6,817(+/- 1,27 %) 6,523(+/-11,96 %) 4,31 %
16 2,930(+/- 1,07 %) 2,911(+/- 1,08 %) 0,66 %
32 2,735(+/- 1,71 %) 2,725(+/- 1,53 %) 0,37 %
64 2,702(+/- 0,32 %) 2,717(+/- 1,07 %) -0,53 %
128 3,533(+/-14,66 %) 3,123(+/-12,47 %) 11,59 %
256 3,918(+/-19,93 %) 3,390(+/- 5,93 %) 13,47 %

The significant improvement for 128 and 256 should be taken with care
because of some instabilities over iterations without the patchset.

The table below shows figures of the classification of sched group during
load balance (idle, newly or busy lb) with the disribution according to
the number of running tasks for:
hackbench -l 640 -g 4 on octo cores

tip/sched/core +patchset
state
has spare 3973 1934
nr_running
0 1965 1858
1 518 56
2 369 18
3 270 2
4+ 851 0

fully busy 546 1018
nr_running
0 0 0
1 546 1018
2 0 0
3 0 0
4+ 0 0

overloaded 2109 3056
nr_running
0 0 0
1 0 0
2 241 483
3 170 348
4+ 1698 2225

total 6628 6008

Without the patchset, there is a significant number of time that a CPU has
spare capacity with more than 1 running task. Although this is a valid
case, this is not a state that should often happen when 160 tasks are
competing on 8 cores like for this test. The patchset fixes the situation
by taking into account the runnable_avg, which stays high after the
migration of a task on another CPU.

Changes since RFC:
- fix come comment and typo
- split in 2 patches the removale of runnable_load_avg and the addition of
runnbale_avg

Vincent Guittot (5):
sched/fair: Reorder enqueue/dequeue_task_fair path
sched/numa: Replace runnable_load_avg by load_avg
sched/pelt: Remove unused runnable load average
sched/pelt: Add a new runnable average signal
sched/fair: Take into account runnable_avg to classify group


include/linux/sched.h | 33 +++--
kernel/sched/core.c | 2 -
kernel/sched/debug.c | 17 +--
kernel/sched/fair.c | 337 ++++++++++++++++++++++--------------------
kernel/sched/pelt.c | 45 +++---
kernel/sched/sched.h | 29 +++-
6 files changed, 247 insertions(+), 216 deletions(-)

--
2.17.1

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