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Subject[PATCH v3 00/13] sched: Clean-ups and asymmetric cpu capacity support

The scheduler is currently not doing much to help performance on systems with
asymmetric compute capacities (read ARM big.LITTLE). This series improves the
situation with a few tweaks mainly to the task wake-up path that considers
compute capacity at wake-up and not just whether a cpu is idle for these
systems. This gives us consistent, and potentially higher, throughput in
partially utilized scenarios. SMP behaviour and performance should be

Test 0:
for i in `seq 1 10`; \
do sysbench --test=cpu --max-time=3 --num-threads=1 run; \
done \
| awk '{if ($4=="events:") {print $5; sum +=$5; runs +=1}} \
END {print "Average events: " sum/runs}'

Target: ARM TC2 (2xA15+3xA7)

(Higher is better)
tip: Average events: 151.8
patch: Average events: 217.9

Target: ARM Juno (2xA57+4xA53)

(Higher is better)
tip: Average events: 1737.7
patch: Average events: 1952.5

Test 1:
perf stat --null --repeat 10 -- \
perf bench sched messaging -g 50 -l 5000

Target: Intel IVB-EP (2*10*2)

tip: 4.632455615 seconds time elapsed ( +- 0.84% )
patch: 4.532470694 seconds time elapsed ( +- 1.28% )

Target: ARM TC2 A7-only (3xA7) (-l 1000)

tip: 61.554834175 seconds time elapsed ( +- 0.11% )
patch: 62.633350367 seconds time elapsed ( +- 0.12% )


Active migration of tasks away from small capacity cpus isn't addressed
in this set although it is necessary for consistent throughput in other
scenarios on asymmetric cpu capacity systems.

The infrastructure to enable capacity awareness for arm64 and arm is not
provided here but will be based on Juri's DT bindings patch set [1]. A
combined preview branch is available [2]. Test results above a based on

[2] git:// capacity_awareness_v3_arm64_v1

Patch 1-4: Generic fixes and clean-ups.
Patch 5-13: Improve capacity awareness.

Tested-by: Koan-Sin Tan <>
Tested-by: Keita Kobayashi <>


- Changed SD_ASYM_CPUCAPACITY sched_domain flag semantics as suggested
by PeterZ.

- Dropped arm specific patches for setting cpu capacity as these are
superseded by Juri's patches [2].

- Changed capacity-aware pulling during load-balance to use sched_group
min capacity instead of max as suggested by Sai.


- Dropped patch ignoring wakee_flips for pid=0 for now as we can not
distinguish cpu time processing irqs from idle time.

- Dropped disabling WAKE_AFFINE as suggested by Vincent to allow more
scenarios to use fast-path (select_idle_sibling()). Asymmetric wake
conditions adjusted accordingly.

- Changed use of new SD_ASYM_CPUCAPACITY slightly. Now enables

- Minor clean-ups and rebased to more recent tip/sched/core.


Dietmar Eggemann (1):
sched: Store maximum per-cpu capacity in root domain

Morten Rasmussen (12):
sched: Fix power to capacity renaming in comment
sched/fair: Consistent use of prev_cpu in wakeup path
sched/fair: Optimize find_idlest_cpu() when there is no choice
sched/core: Remove unnecessary null-pointer check
sched: Introduce SD_ASYM_CPUCAPACITY sched_domain topology flag
sched/core: Pass child domain into sd_init
sched: Enable SD_BALANCE_WAKE for asymmetric capacity systems
sched/fair: Let asymmetric cpu configurations balance at wake-up
sched/fair: Compute task/cpu utilization at wake-up more correctly
sched/fair: Consider spare capacity in find_idlest_group()
sched: Add per-cpu min capacity to sched_group_capacity
sched/fair: Avoid pulling tasks from non-overloaded higher capacity

include/linux/sched.h | 3 +-
kernel/sched/core.c | 37 +++++++--
kernel/sched/fair.c | 213 ++++++++++++++++++++++++++++++++++++++++++++------
kernel/sched/sched.h | 5 +-
4 files changed, 227 insertions(+), 31 deletions(-)


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