[PATCH v5 00/10] track CPU utilization

Vincent Guittot
2018-05-25T13:12:41Z

This patchset initially tracked only the utilization of RT rq. During
OSPM summit, it has been discussed the opportunity to extend it in order
to get an estimate of the utilization of the CPU.

- Patches 1-3 correspond to the content of patchset v4 and add utilization
tracking for rt_rq.

When both cfs and rt tasks compete to run on a CPU, we can see some frequency
drops with schedutil governor. In such case, the cfs_rq's utilization doesn't
reflect anymore the utilization of cfs tasks but only the remaining part that
is not used by rt tasks. We should monitor the stolen utilization and take
it into account when selecting OPP. This patchset doesn't change the OPP
selection policy for RT tasks but only for CFS tasks

A rt-app use case which creates an always running cfs thread and a rt threads
that wakes up periodically with both threads pinned on same CPU, show lot of
frequency switches of the CPU whereas the CPU never goes idles during the
test. I can share the json file that I used for the test if someone is
interested in.

For a 15 seconds long test on a hikey 6220 (octo core cortex A53 platfrom),
the cpufreq statistics outputs (stats are reset just before the test) :
$ cat /sys/devices/system/cpu/cpufreq/policy0/stats/total_trans
without patchset : 1230
with patchset : 14

If we replace the cfs thread of rt-app by a sysbench cpu test, we can see
performance improvements:

- Without patchset :
Test execution summary:
total time: 15.0009s
total number of events: 4903
total time taken by event execution: 14.9972
per-request statistics:
min: 1.23ms
avg: 3.06ms
max: 13.16ms
approx. 95 percentile: 12.73ms

Threads fairness:
events (avg/stddev): 4903.0000/0.00
execution time (avg/stddev): 14.9972/0.00

- With patchset:
Test execution summary:
total time: 15.0014s
total number of events: 7694
total time taken by event execution: 14.9979
per-request statistics:
min: 1.23ms
avg: 1.95ms
max: 10.49ms
approx. 95 percentile: 10.39ms

Threads fairness:
events (avg/stddev): 7694.0000/0.00
execution time (avg/stddev): 14.9979/0.00

The performance improvement is 56% for this use case.

- Patches 4-5 add utilization tracking for dl_rq in order to solve similar
problem as with rt_rq

- Patches 6 uses dl and rt utilization in the scale_rt_capacity() and remove
dl and rt from sched_rt_avg_update

- Patches 7-8 add utilization tracking for interrupt and use it select OPP
A test with iperf on hikey 6220 gives:
w/o patchset w/ patchset
Tx 276 Mbits/sec 304 Mbits/sec +10%
Rx 299 Mbits/sec 328 Mbits/sec +09%

8 iterations of iperf -c server_address -r -t 5
stdev is lower than 1%
Only WFI idle state is enable (shallowest arm idle state)

- Patches 9 removes the unused sched_avg_update code

- Patch 10 removes the unused sched_time_avg_ms

Change since v3:
- add support of periodic update of blocked utilization
- rebase on lastest tip/sched/core

Change since v2:
- move pelt code into a dedicated pelt.c file
- rebase on load tracking changes

Change since v1:
- Only a rebase. I have addressed the comments on previous version in
patch 1/2

Vincent Guittot (10):
sched/pelt: Move pelt related code in a dedicated file
sched/rt: add rt_rq utilization tracking
cpufreq/schedutil: add rt utilization tracking
sched/dl: add dl_rq utilization tracking
cpufreq/schedutil: get max utilization
sched: remove rt and dl from sched_avg
sched/irq: add irq utilization tracking
cpufreq/schedutil: take into account interrupt
sched: remove rt_avg code
proc/sched: remove unused sched_time_avg_ms

include/linux/sched/sysctl.h | 1 -
kernel/sched/Makefile | 2 +-
kernel/sched/core.c | 38 +---
kernel/sched/cpufreq_schedutil.c | 24 ++-
kernel/sched/deadline.c | 7 +-
kernel/sched/fair.c | 381 +++----------------------------------
kernel/sched/pelt.c | 395 +++++++++++++++++++++++++++++++++++++++
kernel/sched/pelt.h | 63 +++++++
kernel/sched/rt.c | 10 +-
kernel/sched/sched.h | 57 ++++--
kernel/sysctl.c | 8 -
11 files changed, 563 insertions(+), 423 deletions(-)
create mode 100644 kernel/sched/pelt.c
create mode 100644 kernel/sched/pelt.h

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2.7.4