[dpdk-dev] If 1 KVM Guest loads the virtio-pci, on top of dpdkvhostuser OVS socket interface, it slows down everything!

[Martinx - ジェームズ]

Guys,

 I'm seeing a strange problem here, in my OVS+DPDK deployment, on top of
Ubuntu 16.04 (DPDK 2.2 and OVS 2.5).

 Here is what I'm trying to do: run OVS with DPDK at the host, for KVM
Guests that also, will be running more DPDK Apps.

 The host have 2 x 10G NICs, for OVS+DPDK and each KVM Guest receives its
own VLAN tagged traffic (or all tags).

 There is an IXIA Traffic Generator sending 10G of traffic on both
directions (20G total).

 Exemplifying, the problem is, lets say that I already have 2 VMs (or 10)
running DPDK Apps (on top of dpdkvhostuser), everything is working as
expected, then, if I boot the 3rd (or 11) KVM Guest, the OVS+DPDK bridge at
the host, slows down, a lot! The 3rd (or 11) VM affects not only the host,
but also, all the other neighbors VMs!!!

 NOTE: This problem appear since the boot of VM 1.

 Soon as you, inside of the 3rd VM, bind the VirtIO NIC to the
DPDK-Compative Drivers, the speed comes back to normal. If you bind it back
to "virtio-pci", boom! The OVS+DPDK at the host and all VMs loses too much
speed.

 This problem is detailed at the following bug report:

--
The OVS+DPDK dpdkvhostuser socket bridge, only works as expected, if the
KVM Guest also have DPDK drivers loaded:

https://bugs.launchpad.net/ubuntu/+source/openvswitch/+bug/1577256
--

 Also, I've recorded a ~15 min screen cast video about this problem, so,
you guys can see exactly what is happening here.

https://www.youtube.com/v/yHnaSikd9XY?version=3&vq=hd720&autoplay=1

 * At 5:25, I'm starting a VM that will boot up and load a DPDK App;

 * At 5:33, OVS+DPDK is messed up, it loses speed;
   The KVM running with virtio-pci drivers breaks OVS+DPDK at the host;

 * At 6:50, DPDK inside of the KVM guest loads up its drivers, kicking
"virtio-pci", speed back to normal at the host;

 * At 7:43, started another KVM Guest, now, while virtio-pci driver is
running, the OVS+DPDK at the host and the other VM, are very, very slow;

 * At 8:52, the second VM loads up DPDK Drivers, kicking virtio-pci, the
speed is back to normal at the host, and on the other VM too;

 * At 10:00, the Ubuntu VM loads up virtio-pci drivers on its boot, the
speed dropped at the hosts and on the other VMs;

 * 11:57, I'm starting "service dpdk start" inside of the Ubuntu guest, to
kick up virtio-pci, and bang! Speed is back to normal everywhere;

 * 12:51, I'm trying to unbind the DPDK Drivers and return the virtio-pci,
I forgot the syntax while recording the video, which is: "dpdk_nic_bind -b
<ID> virtio-pci", so, I just rebooted it. But both "reboot" or "rebind to
virtio-pci" triggers the bug.


NOTE: I tried to subscriber to qemu-devel but, it is not working, I'm not
receiving the confirmation e-mail, while qemu-stable worked. I don't know
if it worth sending it to Linux Kernel too...


Regards,
Thiago