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Re: [Discuss-gnuradio] UDP Sink sending bursty packets

From: Jeff Long
Subject: Re: [Discuss-gnuradio] UDP Sink sending bursty packets
Date: Sun, 4 Mar 2018 19:46:31 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2
I can't think of anything else within the GR core. The scheduler tries to maximize sample throughput, but doesn't try to do any kind of pacing.
It sounds like whatever is receiving the UDP packets is operating at its limits, assuming it would work if the packets were evenly paced. Do you know whether the receiver can handle this data rate at all? Or does it just have a very small RX buffer?
You might be able to get the Linux stack to help using tc (traffic control), depending on the rates you're dealing with. 

On 03/04/2018 07:23 PM, Firdavs Pulat wrote:
Setting it on the UDP itself didn't change the behavior either. Do you (or anyone else) have any other ideas? 

Thank you
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On Sun, Mar 4, 2018 at 5:16 PM, Jeff Long <address@hidden <mailto:address@hidden>> wrote: 

    I think you'd want to set that on the UDP sink itself.

    On 03/04/2018 01:30 PM, Firdavs Pulat wrote:

        Thanks for the suggestion, Jeff. Unfortunately, that didn't seem
        to help. I still see bursty packet transmission.

        Btw, currently I have: USRP source --> Low-Pass Filter -->
        ComplexToInterleavedShort --> Endian Swap --> UDP Sink. I added
        the set_max_noutput_items line at the output of the Endian Swap
        block since that would be the input to UDP. Is that the only
        place where I would have to make that change, or on all the blocks?

        Thanks!


        
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        On Sun, Mar 4, 2018 at 6:44 AM, Jeff Long <address@hidden
        <mailto:address@hidden> <mailto:address@hidden
        <mailto:address@hidden>>> wrote:

             Try yourblock.set_max_noutput_items(1024/itemsize)


             On 03/03/2018 09:57 PM, Firdavs Pulat wrote:

                 Hello everyone,

                 I have a B200mini device I'm communicating over USB to a pc
                 which is running the gnuradio software. The gnuradio
        does some
                 processing (e.g., low-pass filtering, data type conversion,
                 etc), and finally gets to the UDP sink block where
        packets are
                 generated and sent through Ethernet to an external
        device. The
                 issue I'm having is that, in the UDP block,
                 noutput_items*d_itemsize size is alot larger than the UDP
                 payload size (1024 bytes). So, UDP gets 4-6K worth of
        bytes and
                 bursts it all out really fast (I can see this behavior in
                 Wireshark), then waits to buffer up another 4-6K bytes, and
                 sends it all out really fast. This process then
        continues. Is
                 there a way to smooth this out so that it's not
        bursting bunch
                 of packets all at once? Otherwise the external device
        isn't able
                 to keep up and it's leading to tons of dropped packets.

                 I tried setting the max output buffer in python but I
        get this
                 warning when I run: gr::log :WARN: flat_flowgraph - Block
                 (endian_swap_impl0) max output buffer set to 2048
        instead of
                 requested 512.

                 Any ideas on what I can do to change this behaviour?

                 Thanks!



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