RM500Q slow with qmi_wwan, fast with proprietary

[Sebastian Sjöholm]

Hi,

Using RM500Q-GL with QMI/QMUX can do 1,4Gbps on TCP and UDP without any issues. Haven’t tried via MM, only direct with QMI/QMUX (qmi_wwan).

-Sebastian

@Mobile

> On 11 Aug 2022, at 09:59, Bjørn Mork <bjorn at mork.no> wrote:
> 
> Nick <mips171 at icloud.com> writes:
> 
>> Hey,
>> 
>> I am testing a Quectel RM500Q on OpenWrt master, and have noticed to
>> my surprise that the speed is much slower when using the qmi_wwan with
>> MM than it is when using qmi_wwan_q and quectel-CM (Quectel’s
>> proprietary driver and connection manager).
> 
> This is sort of expected since the qmi_wwan driver will use one USB
> transaction per IP packet whereas the qmi_wwan_q will buffer a number of
> packets per transaction.
> 
> There is some built-in support for MAP (RMNET muxing, which implies
> buffering) in qmi_wwan.  But I recommend using the more recent rmnet
> driver for that, with qmi_wwan in pass-throuh mode.  This is supported
> by recent ModemManager/libqmi.  Ref
> https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/447
> 
>> Under good signal conditions the speed tops out at around 100Mbps on
>> qmi_wwan + MM (and is a little bit faster when in MBIM mode with MM),
>> but switching to qmi_wwan_q and quectel_CM it gets the expected
>> 700Mbps+ where I am. Is there an easy explanation for this? Any
>> suggestions as to what I can change to get speeds equivalent to the
>> proprietary stack?
> 
> I'm a little surprised that you don't get better numbers in MBIM mode.
> It should have the same advantages as qmi_wwan_q or qmi_wwan+rmnet. I
> must admit that I haven't done any seriuos testing of this theory myself
> though.  But "A little bit faster than 100Mbps" is unexpectedly slow.
> I'm pretty sure we can do much better than that in MBIM mode.
> 
> What kind of hardware is the host running?  Maybe we have some alignment
> issue punishing this hardware?  Or maybe the buffers we use are
> sub-optimal for thise host+device combo?  You could try to adjust some
> of the writable settings in /sys/class/net/wwan0/cdc_ncm/ (replace wwan0
> with your interface name)
> 
> 
> 
> Bjørn