Messages in this thread | | | From | Vincent Guittot <> | Subject | [PATCH v2 0/8] sched/fair: rework the CFS load balance | Date | Thu, 1 Aug 2019 16:40:16 +0200 |
| |
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 separatly 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 metrics 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.
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 125665 +/-0.61% 125455 +/-0.62% (-0.17%)
hackbench -l (256000/#grp) -g #grp 1 groups 15.263 +/-3.53% 13.776 +/-3.30% (+9.74%) 4 groups 5.852 +/-0.57% 5.340 +/-8.03% (+8.75%) 16 groups 3.097 +/-1.08% 3.246 +/-0.97% (-4.81%) 32 groups 2.882 +/-1.04% 2.845 +/-1.02% (+1.29%) 64 groups 2.809 +/-1.30% 2.712 +/-1.17% (+3.45%) 128 groups 3.129 +/-9.74% 2.813 +/-6.22% (+9.11%) 256 groups 3.559 +/-11.07% 3.020 +/-1.75% (+15.15%)
dbench 1 groups 330.897 +/-0.27% 330.612 +/-0.77% (-0.09%) 4 groups 932.922 +/-0.54% 941.817 +/*1.10% (+0.95%) 16 groups 1932.346 +/-1.37% 1962.944 +/-0.62% (+1.58%) 32 groups 2251.079 +/-7.93% 2418.531 +/-0.69% (+7.44%) 64 groups 2104.114 +/-9.67% 2348.698 +/-11.24% (+11.62%) 128 groups 2093.756 +/-7.26% 2278.156 +/-9.74% (+8.81%) 256 groups 1216.736 +/-2.46% 1665.774 +/-4.68% (+36.91%)
tip/sched/core sha1: a1dc0446d649 ('sched/core: Silence a warning in sched_init()')
Changes since v1: - fixed some bugs - Used switch case - Renamed env->src_grp_type to env->balance_type - split patches in smaller ones - added comments
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 sched/fair: evenly spread tasks when not overloaded sched/fair: use utilization to select misfit task
kernel/sched/fair.c | 769 ++++++++++++++++++++++++++++----------------------- kernel/sched/sched.h | 2 +- 2 files changed, 419 insertions(+), 352 deletions(-)
-- 2.7.4
| |