libvirt users - May 2016 - 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


 + 30 210 667 7689

  <mailto:geopar@intracom-telecom.com> geopar@intracom-telecom.com


 19.7 km Markopoulou Ave 19002 Peania, Athens, Greece

	

 

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