CPU pinning in KVM

[cesarpk]

Hi to all.

I have a server with 2 processors of 10 cores and 20 sub-threads (Hyperthreading).

My preoccupation is with the CPU pinning in KVM, i want to reach the max of performance possible taking advantage the cache of processor, and I need to know what configuration should i apply on PVE for get this best performance?.

Please if anybody can explain me how apply the configuration in PVE (I will be using a data base into the KVM VM).

Best regards
Cesar

 

[zima]

Hi,
use: numactl -H
it will give you output with your processors

#available: 4 nodes (0-3)
#node 0 cpus: 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60
#node 0 size: 32754 MB
#node 0 free: 2407 MB
#node 1 cpus: 1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61
#node 1 size: 32768 MB
#node 1 free: 1926 MB
#node 2 cpus: 2 6 10 14 18 22 26 30 34 38 42 46 50 54 58 62
#node 2 size: 32768 MB
#node 2 free: 2615 MB
#node 3 cpus: 3 7 11 15 19 23 27 31 35 39 43 47 51 55 59 63
#node 3 size: 32768 MB
#node 3 free: 1593 MB
#node distances:
#node 0 1 2 3
# 0: 10 20 20 20
# 1: 20 10 20 20
# 2: 20 20 10 20
# 3: 20 20 20 10


then use:
taskset -a -pc 3,7,11,15,19,23,27,31,35,39,43,47,51,55,59,63 [proces_pid]

it will pin your kvm process to specific processor/cores, do this with all threads from specific kvm machine.

 

[cesarpk]

Hi zima.

Thank you very much for your reply, I value it very much.

Please let me to do a comments and some questions:

- First, the VM is a MS Windows-Server with MS SQL-Server.
- Second, i want to assign all cores and threads of my hardware to my VM.
- Moreover, sorry for the inconvenience, but I do not understand what you are saying, could you be more clear?
For example:
1) How i should apply the "taskset" for that the changes be permanent?.
2) Node ¿? ¿? ¿? ... is a node a processor socket?

Please have a little patience for me, is the first time that i work in this topic.

Best regards.
Cesar

 

[zima]

your output of numactl -H should looks like this:


node 0 cpus: 0 2 4 6 8 10 12 14 16 18
...
node 1 cpus: 1 3 5 7 9 11 13 15 17 19


on intel platform phisical cores are counted first interleaved between cpu sockets(nodes) then logical cores in the same fashion.


phisical cores of cpu0 are: 0 2 4 6 8
logical cores of cpu0 are: 10 12 14 16 18


let's assume that we have kvm machine with 4 cores so this machine will generate 4 pids.


exaple of taskset use:


taskset -a -pc 0,2,4,6 our_kvm_pid
and repeat this 4x for all pids
this will give us kvm machine working on 4 phisical cores of cpu0


taskset -a -pc 0,2,10,12 our_kvm_pid
and repeat this 4x for all pids
this will give us kvm machine working on 2 phisical cores and 2 logical cores of cpu0

 

[Bytales]

Hy, what is [proces_pid] ?
Can you give us an example how to learn the proces PID for a given VM with an id of 100 ?

Do we Need to run this command everytime we start ProxMox, and before the VMs are started ?

 

[LnxBil]

Hy, what is [proces_pid] ?
Can you give us an example how to learn the proces PID for a given VM with an id of 100 ?

Do we Need to run this command everytime we start ProxMox, and before the VMs are started ?

You can also use the NUMA flag to pin it to a numa group:

https://pve.proxmox.com/wiki/NUMA