Scheduler-driven CPU frequency selection hopes to exploit both
per-task and global information in the scheduler to improve frequency
selection policy and achieve lower power consumption, improved
responsiveness/performance, and less reliance on heuristics and
tunables. For further discussion of this integration see [0].
This patch series implements a cpufreq governor which collects CPU
capacity requests from the fair, realtime, and deadline scheduling
classes. The fair and realtime scheduling classes are modified to make
these requests. The deadline class is not yet modified to make CPU
capacity requests.
Changes in this series since RFCv6 [1], posted December 9, 2015:
Patch 3, sched: scheduler-driven cpu frequency selection
- Added Kconfig dependency on IRQ_WORK.
- Reworked locking.
- Make throttling optional - it is not required in order to ensure that
the previous frequency transition is complete.
- Some fixes in cpufreq_sched_thread related to the task state.
- Changes to support mixed fast and slow path operation.
Patch 7: sched/fair: jump to max OPP when crossing UP threshold
- move sched_freq_tick() call so rq lock is still held
Patch 9: sched/deadline: split rt_avg in 2 distincts metrics
- RFCv6 calculated DL capacity from DL task parameters, RFCv7 restores
the original method of calculation but keeps DL capacity separate
Patch 10: sched: rt scheduler sets capacity requirement
- change #ifdef from CONFIG_SMP, trivial cleanup
Profiling results:
Performance profiling has been done by using rt-app [2] to generate
various periodic workloads with a particular duty cycle. The time to
complete the busy portion of the duty cycle is measured and overhead
is calculated as
overhead = (busy_duration_test_gov - busy_duration_perf_gov)/
(busy_duration_pwrsave_gov - busy_duration_perf_gov)
This shows as a percentage how close the governor is to running the
workload at fmin (100%) or fmax (0%). The number of times the busy
duration exceeds the period of the periodic workload (an "overrun") is
also recorded. In the table below the performance of the ondemand
(sampling_rate = 20ms), interactive (default tunables), and
scheduler-driven governors are evaluated using these metrics. The test
platform is a Samsung Chromebook 2 ("Peach Pi"). The workload is
affined to CPU0, an A15 with an fmin of 200MHz and an fmax of
1.8GHz. The interactive governor was incorporated/adapted from [3]. A
branch with the interactive governor and a few required dependency
patches for ARM is available at [4].
More detailed explanation of the columns below:
run: duration at fmax of the busy portion of the periodic workload in msec
period: duration of the entire period of the periodic workload in msec
loops: number of iterations of the periodic workload tested
OR: number of instances of overrun as described above
OH: overhead as calculated above
SCHED_OTHER workload:
wload parameters ondemand interactive sched
run period loops OR OH OR OH OR OH
1 100 100 0 62.07% 0 100.02% 0 78.49%
10 1000 10 0 21.80% 0 22.74% 0 72.56%
1 10 1000 0 21.72% 0 63.08% 0 52.40%
10 100 100 0 8.09% 0 15.53% 0 17.33%
100 1000 10 0 1.83% 0 1.77% 0 0.29%
6 33 300 0 15.32% 0 8.60% 0 17.34%
66 333 30 0 0.79% 0 3.18% 0 12.26%
4 10 1000 0 5.87% 0 10.21% 0 6.15%
40 100 100 0 0.41% 0 0.04% 0 2.68%
400 1000 10 0 0.42% 0 0.50% 0 1.22%
5 9 1000 2 3.82% 1 6.10% 0 2.51%
50 90 100 0 0.19% 0 0.05% 0 1.71%
500 900 10 0 0.37% 0 0.38% 0 1.82%
9 12 1000 6 1.79% 1 0.77% 0 0.26%
90 120 100 0 0.16% 1 0.05% 0 0.49%
900 1200 10 0 0.09% 0 0.26% 0 0.62%
SCHED_FIFO workload:
wload parameters ondemand interactive sched
run period loops OR OH OR OH OR OH
1 100 100 0 39.61% 0 100.49% 0 99.57%
10 1000 10 0 73.51% 0 21.09% 0 96.66%
1 10 1000 0 18.01% 0 61.46% 0 67.68%
10 100 100 0 31.31% 0 18.62% 0 77.01%
100 1000 10 0 58.80% 0 1.90% 0 15.40%
6 33 300 251 85.99% 0 9.20% 1 30.09%
66 333 30 24 84.03% 0 3.38% 0 33.23%
4 10 1000 0 6.23% 0 12.21% 10 11.54%
40 100 100 100 62.08% 0 0.11% 1 11.85%
400 1000 10 10 62.09% 0 0.51% 0 7.00%
5 9 1000 999 12.29% 1 6.03% 0 0.04%
50 90 100 99 61.47% 0 0.05% 2 6.53%
500 900 10 10 43.37% 0 0.39% 0 6.30%
9 12 1000 999 9.83% 0 0.01% 14 1.69%
90 120 100 99 61.47% 0 0.01% 28 2.29%
900 1200 10 10 43.31% 0 0.22% 0 2.15%
Note that at this point RT CPU capacity is measured via rt_avg. For
the above results sched_time_avg_ms has been set to 50ms.
Known issues:
- More testing with real world type workloads, such as UI workloads and
benchmarks, is required.
- The power side of the characterization is in progress.
- Deadline scheduling class does not yet make CPU capacity requests.
- Not sure what's going on yet with the ondemand numbers above, it seems like
there may a regression with ondemand and RT tasks.
Dependencies:
Frequency invariant load tracking is required. For heterogeneous
systems such as big.Little, CPU invariant load tracking is required as
well. The required support for ARM platforms along with a patch
creating tracepoints for cpufreq_sched is located in [5].
References:
[0] http://article.gmane.org/gmane.linux.kernel/1499836
[1] http://thread.gmane.org/gmane.linux.power-management.general/69176
[2] https://git.linaro.org/power/rt-app.git
[3] https://lkml.org/lkml/2015/10/28/782
[4]
https://git.linaro.org/people/steve.muckle/kernel.git/shortlog/refs/heads/interactive
[5]
https://git.linaro.org/people/steve.muckle/kernel.git/shortlog/refs/heads/sched-freq-rfcv7
Juri Lelli (3):
sched/fair: add triggers for OPP change requests
sched/{core,fair}: trigger OPP change request on fork()
sched/fair: cpufreq_sched triggers for load balancing
Michael Turquette (2):
cpufreq: introduce cpufreq_driver_is_slow
sched: scheduler-driven cpu frequency selection
Morten Rasmussen (1):
sched: Compute cpu capacity available at current frequency
Steve Muckle (1):
sched/fair: jump to max OPP when crossing UP threshold
Vincent Guittot (3):
sched: remove call of sched_avg_update from sched_rt_avg_update
sched/deadline: split rt_avg in 2 distincts metrics
sched: rt scheduler sets capacity requirement
drivers/cpufreq/Kconfig | 21 ++
drivers/cpufreq/cpufreq.c | 6 +
include/linux/cpufreq.h | 12 ++
include/linux/sched.h | 8 +
kernel/sched/Makefile | 1 +
kernel/sched/core.c | 43 +++-
kernel/sched/cpufreq_sched.c | 459 +++++++++++++++++++++++++++++++++++++++++++
kernel/sched/deadline.c | 2 +-
kernel/sched/fair.c | 108 +++++-----
kernel/sched/rt.c | 48 ++++-
kernel/sched/sched.h | 120 ++++++++++-
11 files changed, 777 insertions(+), 51 deletions(-)
create mode 100644 kernel/sched/cpufreq_sched.c
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2.4.10
