[Bug 215475] New: RMNET data connection speed would be reduced to about 80-100Mb/s from 150Mb/s if try to re-connect it

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=215475

            Bug ID: 215475
           Summary: RMNET data connection speed would be reduced to about
                    80-100Mb/s from 150Mb/s  if try to re-connect it
           Product: Drivers
           Version: 2.5
    Kernel Version: 5.13.0
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: USB
          Assignee: drivers_usb@kernel-bugs.kernel.org
          Reporter: slark_xiao@163.com
        Regression: No

Created attachment 300251
  --> https://bugzilla.kernel.org/attachment.cgi?id=300251&action=edit
iperf test result

We have a Qualcomm modem device which support MBIM and RMNET over USB.
  For RMNET, the download-link speed would be reduced to 80 Mb/s if re-connect
it once. The expected speed should be 150 Mb/s.
  Test step as below:
  1. Switch device to RMNET USB composition.
  2. Connect it to host PC(kernel 5.13).
  3. Start a data connection with nmcli related settings.
  4. Start a iperf test with simulated network(CMW500). Test result is about
145 Mb/s ,and protocol is TCP.
  5. Disconnect the connection by turning off the signal, setting AT+CFUN=0， or
deleting the data connection in the host.
  6. Re-connect it again.
  7. The TCP iperf test could only reach to about 80-100Mb/s.

  This issue can not reproduced with MBIM port.
  Also, Windows can't reproduce the RMNET issue.

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