Packet rate using QTcpSocket



  • Hi,
    I'm transferring data from a measurement server (Raspberry PI 3) to a client (Windows 7) using a QTcpSocket.
    The data is a few bytes approximately every 30 ms. Each time I call write(data) on the QTcpSocket. The data reaches the client with an increasing delay. Wireshark shows me approximately one package each 200 ms.

    My object and conditions:
    A camera records a frame each 30 ms and the server has to send position information for each frame. Both transfer goes through one common GBit network interface (and a switch). The camera is consuming most of the bandwith, but the VPN link to the server still shows no delay.

    Do you have a hint, how to to transfer the measurement data in real time (ideally once each frame)?



  • Hi @qmmj

    increasing delay means that something needs more time every call. You should search for a structure, string etc. that gets bigger during the run. Could be a memory leak. I e.g. once had a string that got appended to every call which needed more and more time every call.

    -Michael.



  • Hi m.sue,

    that is what I wanted to express: The increasing delay means, that there is somewere a sending queue, which is filled faster (30 ms) than data is removed (200 ms).
    This assumed queue is not part of my written code. A poor solution would be to reduce the filling rate by accumulating multiple data. In that case the delay is still 200 ms and I don't know how this behaves under other conditions.
    A good solution would be to know where this delay comes from and to reduce it.



  • Hi,

    I just learned about the Nagle's algorithm and the QAbstractSocket::LowDelayOption.

    Now it works fine. Thanks.

    qmmj


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