Hi Vincent,
On 14/09/20 11:03, Vincent Guittot wrote: > 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. > Few nitpicks from my end, but no major objections - this looks mostly sane to me. > 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 | 7 +++++-- > kernel/sched/topology.c | 4 ++-- > 2 files changed, 7 insertions(+), 4 deletions(-)
