[PATCH 00/16] sched: Clean-ups and asymmetric cpu capacity support

Morten Rasmussen
2016-05-23T10:58:26Z

Hi,

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 scenarious. SMP behaviour and performance should be
unaffected.

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: 150.2
patch: Average events: 217.9

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

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

tip: 4.831538935 seconds time elapsed ( +- 1.58% )
patch: 4.839951382 seconds time elapsed ( +- 1.01% )

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

tip: 61.406552538 seconds time elapsed ( +- 0.12% )
patch: 61.589263159 seconds time elapsed ( +- 0.22% )

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.

Patch 1-4: Generic fixes and clean-ups.
Patch 5-13: Improve capacity awareness.
Patch 14-16: Arch features for arm to enable asymmetric capacity support.

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

Morten Rasmussen (15):
sched: Fix power to capacity renaming in comment
sched/fair: Consistent use of prev_cpu in wakeup path
sched/fair: Disregard idle task wakee_flips in wake_wide
sched/fair: Optimize find_idlest_cpu() when there is no choice
sched: Introduce SD_ASYM_CPUCAPACITY sched_domain topology flag
sched: Disable WAKE_AFFINE for asymmetric configurations
sched: Make SD_BALANCE_WAKE a topology flag
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 max capacity to sched_group_capacity
sched/fair: Avoid pulling tasks from non-overloaded higher capacity
groups
arm: Set SD_ASYM_CPUCAPACITY for big.LITTLE platforms
arm: Set SD_BALANCE_WAKE flag for asymmetric capacity systems
arm: Update arch_scale_cpu_capacity() to reflect change to define

arch/arm/include/asm/topology.h | 5 +
arch/arm/kernel/topology.c | 25 ++++-
include/linux/sched.h | 3 +-
kernel/sched/core.c | 25 ++++-
kernel/sched/fair.c | 217 ++++++++++++++++++++++++++++++++++++----
kernel/sched/sched.h | 5 +-
6 files changed, 250 insertions(+), 30 deletions(-)

--
1.9.1