Messages in this thread | | | From | Vincent Guittot <> | Subject | [PATCH 0/4 v2] sched/fair: Improve fairness between cfs tasks | Date | Mon, 21 Sep 2020 09:24:20 +0200 |
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When the system doesn't have enough cycles for all tasks, the scheduler must ensure a fair split of those CPUs cycles between CFS tasks. The fairness of some use cases can't be solved with a static distribution of the tasks on the system and requires a periodic rebalancing of the system but this dynamic behavior is not always optimal and the fair distribution of the CPU's time is not always ensured.
The patchset improves the fairness by decreasing the constraint for selecting migratable tasks with the number of failed load balance. This change enables then to decrease the imbalance threshold because 1st LB will try to migrate tasks that fully match the imbalance.
Some tests results:
- small 2 x 4 cores arm64 system
hackbench -l (256000/#grp) -g #grp
grp tip/sched/core +patchset improvement 1 1.420(+/- 11.72 %) 1.382(+/-10.50 %) 2.72 % 4 1.295(+/- 2.72 %) 1.218(+/- 2.97 %) 0.76 % 8 1.220(+/- 2.17 %) 1.218(+/- 1.60 %) 0.17 % 16 1.258(+/- 1.88 %) 1.250(+/- 1,78 %) 0.58 %
fairness tests: run always running rt-app threads monitor the ratio between min/max work done by threads
v5.9-rc1 w/ patchset 9 threads avg 78.3% (+/- 6.60%) 91.20% (+/- 2.44%) worst 68.6% 85.67%
11 threads avg 65.91% (+/- 8.26%) 91.34% (+/- 1.87%) worst 53.52% 87.26%
- large 2 nodes x 28 cores x 4 threads arm64 system
The hackbench tests that I usually run as well as the sp.C.x and lu.C.x tests with 224 threads have not shown any difference with a mix of less than 0.5% of improvements or regressions.
Changes for v2: - rebased on tip/sched/core - added comment for patch 3 - added acked and reviewed tags
Vincent Guittot (4): sched/fair: relax constraint on task's load during load balance sched/fair: reduce minimal imbalance threshold sched/fair: minimize concurrent LBs between domain level sched/fair: reduce busy load balance interval
kernel/sched/fair.c | 13 +++++++++++-- kernel/sched/topology.c | 4 ++-- 2 files changed, 13 insertions(+), 4 deletions(-)
-- 2.17.1
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