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

Kavanagh, Mark B mark.b.kavanagh at intel.com
Wed Oct 26 14:12:41 UTC 2016


>
>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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