Public bug reported:
[Impact]
The latest Xenial update has broken MTU functionality in Xen: specifically,
setting MTUs larger than 1500 fails. This prevents Jumbo Frames and other
features which require larger than 1500 byte MTUs from being used. This can
lead to a failure to sync/connect to other components in the cluster/cloud
which expect higher MTUs and result in unavailable services.
This can be worked around by manually using ethtool to set SCATTER/GATHER
functionality:
- $ sudo ethtool -K $interface_name sg on
The issue is caused by the following commit to the xen-netfront driver:
"xen-netfront: Fix race between device setup and open"
commit f599c64fdf7d9c108e8717fb04bc41c680120da4
Introduced: v4.16-rc1
Reverting the above fix has confirmed that the problem goes away.
The following commits fix this issue in the mainline kernel:
"xen-netfront: Fix mismatched rtnl_unlock"
commit cb257783c2927b73614b20f915a91ff78aa6f3e8
Introduced: v4.18-rc3
"xen-netfront: Update features after registering netdev"
commit 45c8184c1bed1ca8a7f02918552063a00b909bf5
Introduced: v4.18-rc3
[Test Case]
1. Launch a Xen instance using the latest kernel version (e.g. 4.4.0-130,
or 4.4.0-1062-aws)
2. Change MTU to 9000 or other value > 1500.
[Regression Potential]
The kernel patch might not be able to set MTU.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Affects: linux (Ubuntu Xenial)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1781413
Title:
Cannot set MTU higher than 1500 in Xen instance
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