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

[Bodireddy, Bhanuprakash]

I could reproduce the issue and this can be fixed as below

Firstly, the throughput issues observed with other VMs when a new VM is started 
can be fixed using the patch in the thread 
http://openvswitch.org/pipermail/dev/2016-May/071615.html.  I have put up an 
explanation in this thread for the cause of issue especially with multi VM 
setup on OVS DPDK. 

On a Multi VM setup even with the above patch applied, one might see aggregate 
throughput difference when vNIC is bind to igb_uio vs virtio-pci, this is for 
the fact that the interrupt overhead is significantly higher when virtio-pci is 
in use. 

More importantly if you have setup explicit flows matching VM's MAC/IP, 
disabling the flows to the VM that are idle would improve the aggregate 
throughput and lessen the burden on the pmd thread.   'watch -d 
./utilities/ovs-appctl dpctl/show -s' will show no. of packet stats.

Regards,
Bhanu Prakash.


>-----Original Message-----
>From: dev [mailto:address@hidden On Behalf Of Christian
>Ehrhardt
>Sent: Wednesday, May 25, 2016 7:08 AM
>To: Martinx - ジェームズ <address@hidden>
>Cc: <address@hidden> <address@hidden>; dev <address@hidden>;
>address@hidden
>Subject: Re: [ovs-dev] If 1 KVM Guest loads the virtio-pci, on top of
>dpdkvhostuser OVS socket interface, it slows down everything!
>
>Hi again,
>another forgotten case.
>
>I currently I lack the HW to fully reproduce this, but the video summary is
>pretty good and shows the issue in an impressive way.
>
>Also the description is good and here as well I wonder if anybody else could
>reproduce this.
>Any hints / insights are welcome.
>
>P.S. and also again - two list cross posting, but here as well it is yet 
>unclear
>which it belongs to so I'll keep it as well
>
>Christian Ehrhardt
>Software Engineer, Ubuntu Server
>Canonical Ltd
>
>On Sun, May 22, 2016 at 6:35 PM, Martinx - ジェームズ
><address@hidden>
>wrote:
>
>> 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
>>
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