Messages in this thread |  | | From | Morten Rasmussen <> | Subject | [PATCHv2 0/7] sched/fair: Migrate 'misfit' tasks on asymmetric capacity systems | Date | Thu, 15 Mar 2018 14:46:57 +0000 |
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On asymmetric cpu capacity systems (e.g. Arm big.LITTLE) it is crucial for performance that cpu intensive tasks are aggressively migrated to high capacity cpus as soon as those become available. The capacity awareness tweaks already in the wake-up path can't handle this as such tasks might run or be runnable forever. If they happen to be placed on a low capacity cpu from the beginning they are stuck there forever while high capacity cpus may have become available in the meantime.
To address this issue this patch set introduces a new "misfit" load-balancing scenario in periodic/nohz/newly idle balance which tweaks the load-balance conditions to ignore load per capacity in certain cases. Since misfit tasks are commonly running alone on a cpu, more aggressive active load-balancing is needed too.
The fundamental idea of this patch set has been in Android kernels for a long time and is absolutely essential for consistent performance on asymmetric cpu capacity systems.
The patches have been tested on: 1. Arm Juno (r0): 2+4 Cortex A57/A53 2. Hikey960: 4+4 Cortex A73/A53
Test case: Big cpus are always kept busy. Pin a shorter running sysbench tasks to big cpus, while creating a longer running set of unpinned sysbench tasks.
REQUESTS=1000 BIGS="1 2" LITTLES="0 3 4 5"
# Don't care about the score for those, just keep the bigs busy for i in $BIGS; do taskset -c $i sysbench --max-requests=$((REQUESTS / 4)) \ --test=cpu run &>/dev/null & done
for i in $LITTLES; do sysbench --max-requests=$REQUESTS --test=cpu run \ | grep "total time:" & done wait
Results: Single runs with completion time of each task Juno (tip) total time: 1.2608s total time: 1.2995s total time: 1.5954s total time: 1.7463s
Juno (misfit) total time: 1.2575s total time: 1.3004s total time: 1.5860s total time: 1.5871s
Hikey960 (tip) total time: 1.7431s total time: 2.2914s total time: 2.5976s total time: 1.7280s
Hikey960 (misfit) total time: 1.7866s total time: 1.7513s total time: 1.6918s total time: 1.6965s
10 run summary (tracking longest running task for each run) Juno Hikey960 avg max avg max tip 1.7465 1.7469 2.5997 2.6131 misfit 1.6016 1.6192 1.8506 1.9666
Changelog: v2 - Removed redudant condition in static_key enablement. - Fixed logic flaw in patch #2 reported by Yi Yao <yi.yao@intel.com> - Dropped patch #4 as although the patch seems to make sense no benefit has been proven. - Dropped root_domain->overload renaming - Changed type of root_domain->overload to int - Wrapped accesses of rq->rd->overload with READ/WRITE_ONCE - v1 Tested-by: Gaku Inami <gaku.inami.xh@renesas.com>
Morten Rasmussen (3): sched: Add static_key for asymmetric cpu capacity optimizations sched/fair: Add group_misfit_task load-balance type sched/fair: Consider misfit tasks when load-balancing
Valentin Schneider (4): sched/fair: Kick nohz balance if rq->misfit_task sched: Change root_domain->overload type to int sched: Wrap rq->rd->overload accesses with READ/WRITE_ONCE sched/fair: Set sd->overload when misfit
kernel/sched/fair.c | 115 +++++++++++++++++++++++++++++++++++++++--------- kernel/sched/sched.h | 15 +++++-- kernel/sched/topology.c | 9 ++++ 3 files changed, 115 insertions(+), 24 deletions(-)
-- 2.7.4
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