[RFC] QMAP data aggregation support in ModemManager

[Loic Poulain]

On Fri, 26 Feb 2021 at 15:15, Aleksander Morgado
<aleksander at aleksander.es> wrote:
>
> Hey all!
>
> I've been working on updating ModemManager to allow setting up QMAP
> data aggregated links transparently, either with qmi_wwan
> add_mux/del_mux or with qmi_wwan+rmnet (pass_through=Y).
>
> See https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/447
>
> For the qmi_wwan+rmnet logic this MR in libqmi to disable the MAP
> checksum seems to be required, I don't fully understand why yet:
> https://gitlab.freedesktop.org/mobile-broadband/libqmi/-/merge_requests/215
>
> For the qmi_wwan add_mux/del_mux logic, it works quite well without
> any additional thing required, with the limitation of max 4 links for
> now, because we cannot create new links once the master interface is
> already up (so we always precreate 4 link interfaces upon the first
> connection attempt). The MTU of the master link is set to the max data
> aggregation size reported by the modem in this case.
>
> What do you think of these changes? For now, I've made it the default
> to "multiplex=request" when setting up a connection, so that you can
> directly use e.g. NetworkManager to bring up the connection without
> any single change in NetworkManager itself. That may change later on,
> and we may leave the default as "multiplex=none" instead; comments
> welcome on that as well.
>
> Anyone wants to give all this a try? Comments?

Great work Aleksander, I'll be happy to test this (probably next week).
Aggregation offered by QMAP is especially useful for reaching max 5G throughput.

I've heard that some modems support checksum offload, and it seems
already supported on rmnet kernel side (MAPv5). Not sure however how
it needs to be configured for the modem side, maybe via a QMI
wda_set_data_format parameter. On high throughput, the CPU spends
substantial time on checksumming, so it could be useful to have that
at some point.

Regards,
Loic