Hello Yaniv.

Have a new information about this scenario: I have load-balanced the requests between both vNICs, so each is receiving/sending half of the traffic in average and the packet loss although it still exists it lowered to 1% - 2% (which was expected as the CPU to process this traffic is shared by more than one CPU at a time).
However the Load on the VM is still high probably due to the interrupts.

Find below in-line the answers to some of your points:

On 21/03/2017 12:31, Yaniv Kaul wrote:

So there are 2 NUMA nodes on the host? And where are the NICs located?

Tried to search how to check it but couldn't find how. Could you give me a hint ?

 

BTW, since those are virtual interfaces, why do you need two on the same VLAN?

Very good question. It's because of an specific situation where I need to 2 MAC addresses in order to balance the traffic in LAG in a switch which does only layer 2 hashing.

 

Are you using hyper-threading on the host? Otherwise, I'm not sure threads per core would help.

Yes I have hyper-threading enabled on the Host. Is it worth to enable it ?

Thanks
Fernando

On 18/03/2017 12:53, Yaniv Kaul wrote:

On Fri, Mar 17, 2017 at 6:11 PM, FERNANDO FREDIANI <fernando.frediani@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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