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

Vincent Guittot
2022-11-14T10:41:03Z

On Sun, 13 Nov 2022 at 09:51, shrikanth suresh hegde
<sshegde@linux.vnet.ibm.com> wrote:
>
>
> > 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@linux.vnet.ibm.com>

Thanks for the tests and the results

>