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[libvirt-users] vcpupin vs taskset performance difference



Hi all,

 

I am trying to run some performance tests using libvirt 1.2.17. For these tests it is necessary to set a specific affinity for the VCPUs of a running VM.

The problem is, that I noticed a significant performance drop in my metrics when using ‘vcpupin’ from the virsh console instead of running ‘taskset’ natively.

 

Specifically the methods I am comparing are

 

1.       Using native shell

taskset –a –cp $MY_CPUSET $MY_DOMAIN_PID

 

2.       Using virsh console (performance ~30% down)

for all $VCPUs

virsh vcpupin my_domain –cpulist $MY_CPUSET –vcpu $VCPU –live

                virsh emulatorpin my_domain –cpulist $MY_CPUSET –live

 

It seems that the usage of ‘vcpupin’ causes a performance drop even if it is run alongside ‘taskset’ on the same $CPU_SET

 

Functionally everything seems to be working when I check the ‘/proc/’ filesystem

                cat /proc/MY_DOMAIN_PID/*/status | grep Cpus_allowed_list

 

My questions are:

1.       Has anybody else noticed this?

2.       Is this expected based on the implementation details?

3.       Is this a bug that is fixed in a newer libvirt version?

4.       Is there a solution to this issue?

 

 

Thanks,

 

George Paraskevopoulos   

Software Engineer (SDN/NFV)INTRACOM-TELECOM

https://newoldstamp.com/editor/images/phone_g.png + 30 210 667 7689

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https://newoldstamp.com/editor/images/address_g.png 19.7 km Markopoulou Ave 19002 Peania, Athens, Greece

 

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