[virtio-dev] [PATCH] virtio-net: use mtu size as buffer length for big packets

Si-Wei Liu
Tue, 09 Aug 2022 19:08:55 -0000

On 8/9/2022 11:42 AM, Parav Pandit wrote:
>> From: Si-Wei Liu <si-wei.liu at oracle.com>
>> Sent: Tuesday, August 9, 2022 2:39 PM
>> Currently it is not. Not a single patch nor this patch, but the context
for the
>> eventual goal is to allow XDP on a MTU=9000 link when guest users
>> intentionally lower down MTU to 1500.
> Which application benefit by having asymmetry by lowering mtu to 1500 to
send packets but want to receive 9K packets?
I think virtio-net driver doesn't differentiate MTU and MRU, in which
case the receive buffer will be reduced to fit the 1500B payload size
when mtu is lowered down to 1500 from 9000. What I actually tried to say
is that as our current use case (software virtio) supports XDP
applications with 1500 guest mtu and mergeable buffer enabled on a 9000
MTU link, technically it's a legitimate use case regardless of mergeable
buffer capability. Otherwise it's considered to be a usability
regression in driver software side when migrating (not live migrating)
existing user to vdpa, due to lack of hardware implementation of certain
relevant feature.

Thanks,
-Siwei