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jpp_
Tux's lil' helper
Tux's lil' helper


Joined: 23 Oct 2009
Posts: 103
Location: Argentina

PostPosted: Mon Jun 20, 2022 3:18 pm    Post subject: Isolate CPU for kvm Reply with quote

Hello.
I move from systemd to openrc again

And i wish to have a hook qemu working

cat /etc/libvirt/hooks/qemu
Code:
#!/bin/sh

command=$2

if [ "$command" = "started" ]; then
    systemctl set-property --runtime -- system.slice AllowedCPUs=0,1,2,3,4,5,16,17,18,19,20,21
    systemctl set-property --runtime -- user.slice AllowedCPUs=0,1,2,3,4,5,16,17,18,19,20,21
    systemctl set-property --runtime -- init.scope AllowedCPUs=0,1,2,3,4,5,16,17,18,19,20,21
elif [ "$command" = "release" ]; then
    systemctl set-property --runtime -- system.slice AllowedCPUs=0-31
    systemctl set-property --runtime -- user.slice AllowedCPUs=0-31
    systemctl set-property --runtime -- init.scope AllowedCPUs=0-31
fi



How can i do this with openrc?

Regards
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user
Apprentice
Apprentice


Joined: 08 Feb 2004
Posts: 184

PostPosted: Mon Jun 20, 2022 9:22 pm    Post subject: Reply with quote

Hi jpp_
qemu don't support native cpu pinning after years and cgroups setup maybe too hassle so playing with taskset can be useful.
Something like:
Code:

sleep 15 && ps -To spid --no-headers -p $(pidof qemu-system-x86_64) | xargs -n1 taskset --cpu-list --pid 0,1,2,3,4,5,16,17,18,19,20,21

(there can be additional qemu IO worker processes later on)
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szatox
Advocate
Advocate


Joined: 27 Aug 2013
Posts: 2316

PostPosted: Mon Jun 20, 2022 11:42 pm    Post subject: Reply with quote

Haven't tried it, but I think it could be done with cgroups.
Like in, drop the process and cpu cores it's supposed to run on into the same cgroup. If I understand it correctly, the process and all its children spawned afterwards will be pinned to those selected cores and also those cores will be reserved for said processes.
Looks promising.

Taskset is a bit simpler, it can prevent a process from running on some cores, but it's very easy to use, so yeah, it is a good first pick.

I wonder what you're trying to achieve though, why is default scheduling not good enough? Are your processes constantly getting kicked around causing cache misses or something like that?
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jpp_
Tux's lil' helper
Tux's lil' helper


Joined: 23 Oct 2009
Posts: 103
Location: Argentina

PostPosted: Tue Jun 21, 2022 3:05 pm    Post subject: Reply with quote

For what i read, im trying to use one physical part of the cpu with his cache only for the vm, so the host dont see / use it and add latency, and also i use part of the other half to iothread and qemu.

Part of the VM xml
Code:
  <memory unit="KiB">24971520</memory>
  <currentMemory unit="KiB">24971520</currentMemory>
  <vcpu placement="static">16</vcpu>
  <iothreads>2</iothreads>
  <cputune>
    <vcpupin vcpu="0" cpuset="8"/>
    <vcpupin vcpu="1" cpuset="24"/>
    <vcpupin vcpu="2" cpuset="9"/>
    <vcpupin vcpu="3" cpuset="25"/>
    <vcpupin vcpu="4" cpuset="10"/>
    <vcpupin vcpu="5" cpuset="26"/>
    <vcpupin vcpu="6" cpuset="11"/>
    <vcpupin vcpu="7" cpuset="27"/>
    <vcpupin vcpu="8" cpuset="12"/>
    <vcpupin vcpu="9" cpuset="28"/>
    <vcpupin vcpu="10" cpuset="13"/>
    <vcpupin vcpu="11" cpuset="29"/>
    <vcpupin vcpu="12" cpuset="14"/>
    <vcpupin vcpu="13" cpuset="30"/>
    <vcpupin vcpu="14" cpuset="15"/>
    <vcpupin vcpu="15" cpuset="31"/>
    <emulatorpin cpuset="7,23"/>
    <iothreadpin iothread="1" cpuset="6,22"/>
    <iothreadpin iothread="2" cpuset="7,23"/>
    <vcpusched vcpus="0" scheduler="rr" priority="1"/>
    <vcpusched vcpus="1" scheduler="rr" priority="1"/>
    <vcpusched vcpus="2" scheduler="rr" priority="1"/>
    <vcpusched vcpus="3" scheduler="rr" priority="1"/>
    <vcpusched vcpus="4" scheduler="rr" priority="1"/>
    <vcpusched vcpus="5" scheduler="rr" priority="1"/>
    <vcpusched vcpus="6" scheduler="rr" priority="1"/>
    <vcpusched vcpus="7" scheduler="rr" priority="1"/>
    <vcpusched vcpus="8" scheduler="rr" priority="1"/>
    <vcpusched vcpus="9" scheduler="rr" priority="1"/>
    <vcpusched vcpus="10" scheduler="rr" priority="1"/>
    <vcpusched vcpus="11" scheduler="rr" priority="1"/>
    <vcpusched vcpus="12" scheduler="rr" priority="1"/>
    <vcpusched vcpus="13" scheduler="rr" priority="1"/>
    <vcpusched vcpus="14" scheduler="rr" priority="1"/>
    <vcpusched vcpus="15" scheduler="rr" priority="1"/>
    <iothreadsched iothreads="2" scheduler="fifo" priority="98"/>
  </cputune>


Code:
~
 ╰─λ lscpu -e
CPU NODE SOCKET CORE L1d:L1i:L2:L3 ONLINE    MAXMHZ    MINMHZ      MHZ
  0    0      0    0 0:0:0:0          yes 5083.3979 2200.0000 2897.301
  1    0      0    1 1:1:1:0          yes 5083.3979 2200.0000 2200.000
  2    0      0    2 2:2:2:0          yes 5083.3979 2200.0000 3318.368
  3    0      0    3 3:3:3:0          yes 5083.3979 2200.0000 3400.000
  4    0      0    4 4:4:4:0          yes 5083.3979 2200.0000 2200.000
  5    0      0    5 5:5:5:0          yes 5083.3979 2200.0000 2200.000
  6    0      0    6 6:6:6:0          yes 5083.3979 2200.0000 2200.000
  7    0      0    7 7:7:7:0          yes 5083.3979 2200.0000 2200.000
  8    0      0    8 8:8:8:1          yes 5083.3979 2200.0000 3400.000
  9    0      0    9 9:9:9:1          yes 5083.3979 2200.0000 4666.853
 10    0      0   10 10:10:10:1       yes 5083.3979 2200.0000 2200.000
 11    0      0   11 11:11:11:1       yes 5083.3979 2200.0000 2200.000
 12    0      0   12 12:12:12:1       yes 5083.3979 2200.0000 2200.000
 13    0      0   13 13:13:13:1       yes 5083.3979 2200.0000 2200.000
 14    0      0   14 14:14:14:1       yes 5083.3979 2200.0000 3441.394
 15    0      0   15 15:15:15:1       yes 5083.3979 2200.0000 2200.000
 16    0      0    0 0:0:0:0          yes 5083.3979 2200.0000 2200.000
 17    0      0    1 1:1:1:0          yes 5083.3979 2200.0000 2200.000
 18    0      0    2 2:2:2:0          yes 5083.3979 2200.0000 2200.000
 19    0      0    3 3:3:3:0          yes 5083.3979 2200.0000 2200.000
 20    0      0    4 4:4:4:0          yes 5083.3979 2200.0000 2200.000
 21    0      0    5 5:5:5:0          yes 5083.3979 2200.0000 2200.000
 22    0      0    6 6:6:6:0          yes 5083.3979 2200.0000 2200.000
 23    0      0    7 7:7:7:0          yes 5083.3979 2200.0000 2200.000
 24    0      0    8 8:8:8:1          yes 5083.3979 2200.0000 2200.000
 25    0      0    9 9:9:9:1          yes 5083.3979 2200.0000 2200.000
 26    0      0   10 10:10:10:1       yes 5083.3979 2200.0000 2200.000
 27    0      0   11 11:11:11:1       yes 5083.3979 2200.0000 2200.000
 28    0      0   12 12:12:12:1       yes 5083.3979 2200.0000 2200.000
 29    0      0   13 13:13:13:1       yes 5083.3979 2200.0000 2200.000
 30    0      0   14 14:14:14:1       yes 5083.3979 2200.0000 2200.000
 31    0      0   15 15:15:15:1       yes 5083.3979 2200.0000 2200.000
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