Re: [PATCH v7 0/9] Add latency priority for CFS class

[shrikanth suresh hegde]

> This patchset restarts the work about adding a latency priority to describe
> the latency tolerance of cfs tasks.

Hi Vincent.
 
Tested the patches on the power10 machine. It is 80 core system with SMT=8. i.e
total of 640 cpus. on the large workload which mainly interacts with the
database there is minor improvement of 3-5%.

the method followed is creating a cgroup, assigning a latency nice value of -20,
-10, 0 and adding the tasks to procs of the cgroup. outside of cgroup, stress-ng
load is running and it is not set any latency value. stress-ng --cpu=768 -l 50

with microbenchmarks, hackbench the values are more or less the same. for large
process pool of 60, there is 10% improvement. schbench tail latencies show
significant improvement with low and medium load upto 256 groups. only 512
groups shows a slight decline.

Hackbench (Iterations or N=50)
Process             6.1_Base        6.1_Latency_Nice
10                      0.13            0.14
20                      0.18            0.18
30                      0.24            0.25
40                      0.34            0.33
50                      0.40            0.41
60                      0.53            0.49

schbench (Iterations or N=5)

Groups: 1
                    6.1_Base        6.1_Latency_Nice
50.0th:                 10.8             9.8
75.0th:                 12.4            11.4
90.0th:                 14.2            13.2
95.0th:                 15.6            14.6
99.0th:                 27.8            19.0
99.5th:                 38.0            21.6
99.9th:                 66.2            25.4

Groups: 2
                    6.1_Base        6.1_Latency_Nice
50.0th:                 11.2            10.8
75.0th:                 13.2            12.4
90.0th:                 15.0            15.0
95.0th:                 16.6            16.6
99.0th:                 22.4            22.8
99.5th:                 23.8            27.8
99.9th:                 30.2            45.6

Groups: 4
                    6.1_Base        6.1_Latency_Nice
50.0th:                 13.8            11.2
75.0th:                 16.0            13.2
90.0th:                 18.6            15.2
95.0th:                 20.4            16.6
99.0th:                 28.8            21.6
99.5th:                 48.8            25.2
99.9th:                900.2            47.0

Groups: 8
                    6.1_Base        6.1_Latency_Nice
50.0th:                 17.8            14.4
75.0th:                 21.8            17.2
90.0th:                 25.4            20.4
95.0th:                 28.0            22.4
99.0th:                 52.8            28.4
99.5th:                156.4            32.6
99.9th:               1990.2            52.0

Groups: 16
                    6.1_Base        6.1_Latency_Nice
50.0th:                 26.0            21.0
75.0th:                 33.0            27.8
90.0th:                 39.6            34.4
95.0th:                 43.4            38.6
99.0th:                 66.8            48.8
99.5th:                170.6            60.6
99.9th:               3308.8           201.6

Groups: 32
                    6.1_Base        6.1_Latency_Nice
50.0th:                 40.8            38.6
75.0th:                 55.4            52.8
90.0th:                 67.0            64.2
95.0th:                 74.2            71.6
99.0th:                106.0            90.0
99.5th:                323.8           133.0
99.9th:               4789.6           459.2

Groups: 64
                    6.1_Base        6.1_Latency_Nice
50.0th:                 72.6            68.2
75.0th:                103.4            97.8
90.0th:                127.6           120.0
95.0th:                141.2           132.0
99.0th:                343.4           158.4
99.5th:               1609.0           180.8
99.9th:               6571.2           686.6

Groups: 128
                    6.1_Base        6.1_Latency_Nice
50.0th:                147.2           147.2
75.0th:                216.4           217.2
90.0th:                268.4           268.2
95.0th:                300.6           294.8
99.0th:               3500.0           638.6
99.5th:               5995.2          2522.8
99.9th:              10390.4          9451.2

Groups: 256
                    6.1_Base        6.1_Latency_Nice
50.0th:                340.8           333.2
75.0th:                551.8           530.2
90.0th:               3528.4          1919.2
95.0th:               7312.8          5558.4
99.0th:              14630.4         12912.0
99.5th:              17955.2         14950.4
99.9th:              23059.2         20230.4

Groups: 512
                    6.1_Base        6.1_Latency_Nice
50.0th:               1021.8           990.6
75.0th:               9545.6         10044.8
90.0th:              20972.8         21638.4
95.0th:              29971.2         30291.2
99.0th:              42355.2         46707.2
99.5th:              48550.4         52057.6
99.9th:              58867.2         60147.2

Tested-by: shrikanth Hegde <sshegde@xxxxxxxxxxxxxxxxxx>