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

[Yaniv Kaul]

On Fri, Mar 17, 2017 at 6:11 PM, FERNANDO FREDIANI <
fernando.frediani at upx.com> wrote:

> 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 ?
>

I don't see a need for multi-queue for 1Gbps.
Can you share the host statistics, the network configuration, the qemu-kvm
command line, etc.?
What is the difference between NIC1 and NIC2, in the way they are connected
to the outside world?


>
> 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.
>

Load = latest 'top' results? Vs. CPU usage? Can mean a lot of processes
waiting for CPU and doing very little - typical for web servers, for
example. What is occupying the CPU?
Y.


>
> Thanks
> Fernando
>
>
>
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