Comment 0 for bug 1902531

We identified an issue with the Linux netvsc driver when used in IP forwarding mode. The problem is that the RSS hash value is not propagated to the outgoing packet, and so such packets go out on channel 0. This produces an imbalance across outgoing channels, and a possible overload on the single host-side CPU that is processing channel 0. The problem does not occur when Accelerated Networking is used because the packets go out through the Mellanox driver. Because it is tied to IP forwarding, the problem is presumably most likely to be visible in a virtual appliance device that is doing network load balancing or other kinds of packet filtering and redirection.

We would like to request fixes to this issue in 16.04, 18.04 and 20.04.

Two fixes are already in the upstream v5.5+, so they’re already in 5.8.0-1011.11.

For 5.4.0-1031.32, the 2 fixes can apply cleanly:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1fac7ca4e63bf935780cc632ccb6ba8de5f22321
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6f3aeb1ba05d41320e6cf9a60f698d9c4e44348e

For 5.0.0-1036.38, we need 1 more patch applied first, so the list is:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b441f79532ec13dc82d05c55badc4da1f62a6141
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1fac7ca4e63bf935780cc632ccb6ba8de5f22321
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6f3aeb1ba05d41320e6cf9a60f698d9c4e44348e

For 4.15.0-1098.109~16.04.1, the 2 patches can not apply cleanly, so Dexuan backported them here:
https://github.com/dcui/linux/commit/4ed58762a56cccfd006e633fac63311176508795
https://github.com/dcui/linux/commit/40ad7849a6365a5a485f05453e10e3541025e25a
(The 2 patches are on the branch https://github.com/dcui/linux/commits/decui/ubuntu_16.04/linux-azure/Ubuntu-azure-4.15.0-1098.109_16.04.1)