[ovirt-users] Strange network performance on VirtIIO VM NIC

[FERNANDO FREDIANI]

Hello all.

I have a peculiar problem here which perhaps others may have had or know
about and can advise.

I have Virtual Machine with 2 VirtIO NICs. This VM serves around 1Gbps of
traffic with thousands of clients connecting to it. When I do a packet loss
test to the IP pinned to NIC1 it varies from 3% to 10% of packet loss. When
I run the same test on NIC2 the packet loss is consistently 0%.

>From what I gather I may have something to do with possible lack of Multi
Queu VirtIO where NIC1 is managed by a single CPU which might be hitting
100% and causing this packet loss.

Looking at this reference (
https://fedoraproject.org/wiki/Features/MQ_virtio_net) I see one way to
test it is start the VM with 4 queues (for example), but checking on the
qemu-kvm process I don't see option present. Any way I can force it from
the Engine ?

This other reference (
https://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature) points to the
same direction about starting the VM with queues=N

Also trying to increase the TX ring buffer within the guest with ethtool -g
eth0 is not possible.

Oh, by the way, the Load on the VM is significantly high despite the CPU
usage isn't above 50% - 60% in average.

Thanks
Fernando
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