Currently energy calculation in EAS has missed to consider RT pressure, it's quite possible to select CPU for CFS tasks which has high RT pressure and finally accumulate total utilization; as result the other low RT pressure CPUs lose chance to run CFS tasks and reduce contention between CFS and RT tasks, from performance view this is not optimal; furthermore this also harms power data due pack RT task and CFS task on single one CPU is more easily to trigger CPU frequency increasing.
We can measure the summed CPU utilization and calculate the CPU freqency standard deviation to get to if the tasks can be well spreading within the same cluster for middle workload case. So below is the comparison result for video playback on Hikey960 for before and after applied this patch set (Using schedutil CPUFreq governor):
Without Patch Set: With Patch Set:
CPU Min(Util) Mean(Util) Mean(Util) | Min(Util) Mean(Util) Mean(Util) 0 7 67 205 | 8 52 170 1 4 53 227 | 9 47 188 2 4 57 191 | 8 38 192 3 4 35 165 | 16 47 146 s.d. 1.5 13.3 25.9 | 3.9 5.83 20.9
4 0 35 160 | 10 34 129 5 0 24 129 | 0 30 115 6 0 18 123 | 0 18 95 7 0 12 84 | 0 21 73 s.d. 0 9.8 31.2 | 5 7.5 24.4
The standard diviation for CPU utilization mean value has been decreased after applying this patch set (Little cluster: 13.3 vs 5.83, big cluster: 9.8 vs 7.5). This also confirm from the average CPU frequency:
Without Patch Set: With Patch Set: Average Frequency | Average Frequency LITTLT Cluster 737MHz | 646MHz big Cluster 916MHz | 922MHz
Leo Yan (4): sched/fair: Select maximum spare capacity for idle candidate CPUs sched: Introduce cpu_util_sum()/__cpu_util_sum() functions sched/fair: Consider RT pressure for find_best_target() sched/fair: Consider RT/DL pressure for energy calculation
kernel/sched/fair.c | 22 +++++++++++++++++++--- kernel/sched/sched.h | 29 +++++++++++++++++++++++++++++ 2 files changed, 48 insertions(+), 3 deletions(-)
-- 1.9.1