[RFC] QMAP data aggregation support in ModemManager

[Aleksander Morgado]

Hey

> > 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.
>

Please let me know what your tests go!

> 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.
>

I have no idea how that is configured in the modem side either; maybe
we're indeed missing some parameter in the WDA Set Data Format
message, because as soon as I enable MAPv4 the traffic is broken in my
tests: https://gitlab.freedesktop.org/mobile-broadband/libqmi/-/merge_requests/215.
I have seen the MAPv5 patches in the LKML, but haven't tried that
either.

-- 
Aleksander
https://aleksander.es