[ovs-discuss] Vhostports drop issue - related to MTU - Qemu version

[Kapil Adhikesavalu]

Hi Mark,

This commit is already part of 2.6.0 that i am using. Also, when i create
an port with mtu_request, it is creating with the expected mtu, no problems
here.

The issue i am facing is, i am not even able to run traffic through a
PHY-VM-PHY with the default MTU (mtu_request not used).
I am just creating the dpdk and vhostuser ports without mtu_request and all
the packets are getting dropped at vhostuser port

Working scenario:  DPDK16.04 + OVS2.5.9 + qemu 2.4.1 - default MTU 1500
Non-working scenario: * DPDK16.07 + OVS2.6.0* + qemu 2.4.1 - default MTU
1500.

When i reconfigure the default vhostuser mtu to a different value, packet
drop issue stop; Though issue pops up if the VM is rebooted.
I am trying to find why the default config wouldn't work with the above
dpdk,ovs,qemu version ?

Also doing qemu upgrade is resolving the issue - DPDK16.07 + OVS2.6.0 + *qemu
2.6.2* - default MTU 1500.
There are other dependencies for me in upgrading the qemu verson to 2.6.2,
so i am looking for a way to make it work with 2.4.1.

Regards
Kapil.

On Wed, Oct 26, 2016 at 7:42 PM, Kavanagh, Mark B <mark.b.kavanagh at intel.com
> wrote:

> >
> >Hi,
> >
> >Issue Setup:  DPDK 16.07 + OVS 2.6.0 + qemu 2.4.1 : PHY-VM-PHY
> >
> >I am trying to upgrade from (DPDK16.04 + OVS2.5.9), to (DPDK16.07 +
> OVS2.6.0) for jumbo frame
> >support. After the upgrade, all packets are getting dropped on the
> vhostuser port.
> >The dpdk/vhost user ports used here has default MTU of 1500 and packets
> are within the MTU
> >size.
> >
> >Upon few trails, i found configuring the mtu on the vhostuser port is
> somehow fixing the drop
> >issue. Command used : ovs-vsctl set interface vhostuser1
> mtu_request=1400(to any value
> >works).
> >Though even with this, if i reboot the VM, again the drop issue shows up
> and mtu has to be
> >reconfigured/changed on the vhost to get the traffic working.
> >Seems, modifying the mtu value on vhost is internally triggering
> something which resolves the
> >drop issue.
> >
> >I upgraded the qemu to 2.6.2, which resolves the drop issue in the vhost
> ports without any
> >changes to default MTU.
> >I suspect, if its some interop issue with qemu 2.4.1, after the addition
> of jumbo frame
> >support in OVS 2.6.0.
> >
> >Some input on how to debug this will help. is there any dependency on
> dpdk+ovs version with
> >qemu version ?
>
> Hi Kapil,
>
> You should update OvS to the following commit, which resolves the MTU
> issue:
>
>         commit 7c12e20006118e69a98f6840731ebf0c87582b4a
>         Author: Daniele Di Proietto <diproiettod at vmware.com>
>         Date:   Mon Aug 29 19:01:13 2016 -0700
>
>         bridge: Honor 'mtu_request' when port is added.
>
>         'mtu_request' was honored only when the port was reconfigured, not
> when
>          the port was added.
>
>         This commit fixes the problem and improves a testcase to detect
> the bug.
>
> Hope this helps,
> Mark
>
> >
> >i wanted to try dpdk or ovs upgrade alone, instead of both, but it has
> some build
> >dependencies, so i can't try that.
> >My earlier mail on this issue - https://www.mail-
> >archive.com/dev at openvswitch.org/msg71381.html .
> >
> >Regards
> >Kapil.
>
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