RM500Q slow with qmi_wwan, fast with proprietary

[Nick]

Hi Bjørn, 

The hardware is a custom IPQ4019-based board with 512MB RAM, irqbalance running.  It’s not the most powerful hardware out there but handles 500 to 700Mbps quite handily with the Quectel stack. In MBIM mode it gets between 200Mbps to 220Mbps.  All testing is done over ethernet cable of course.  Would there be any settings I should try when in MBIM mode?

I don’t see anything named cdc_ncm in sysfs unfortunately, just the qmi/add|del_mux 

Sebastian, thanks for the information that is hopeful news.  How did you get the QMUX setup without modemmanager?

Best,
Nick

> On 11 Aug 2022, at 17:47, 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