[Libvirt][emulator-cores][dpdk] Emulatorpin cpuset best practices

[Laurent Dumont]

Hey folks,

I am curious to understand a bit more the core use of the emulatorpin CPUs
with libvirt.

For example :

    <vcpupin vcpu='0' cpuset='34'/>
    <vcpupin vcpu='1' cpuset='14'/>
    <vcpupin vcpu='2' cpuset='10'/>
    <vcpupin vcpu='3' cpuset='30'/>
    <emulatorpin cpuset='10,14,30,34'/>

In this case :

   - The VM has 4 vCPUs.
   - Each of the core is pinned to a physical/thread core - 34,14,10,30
   - The emulatorpin is also attached to the same physical CPUs.

In our case :

   - Same setup for cores.
   - Running DPDK inside the virtual machine.
   - The compute/libvirt is using OVS but without DPDK.

What we saw is the following :

   - DPDK is polling two cores at 100% to process packets.
   - From the compute metrics, we see USER %usage at 100% when the
   application starts.
   - From the compute metrics, as traffic increases, we see %SYSTEM going
   up.
   - As %SYSTEM goes up, %USER goes down.

We are not quite sure, but we are wondering if this could cause a direct
impact to the ability of DPDK to process traffic at the same X speed?

   - We can "live" move the emulator CPU to other cores.
   - This seems to be the recommended default setup for VNF/NFV deployments.


Feels like I am missing a piece of the puzzle but gotta start somewhere!

Thanks!
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