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

[CEL]

Hi Firdavs,

I'd fully second what Jeff wrote:
Your flow graph is running barely in real-time. So, GNU Radio's
optimization for throughput (instead of constant latency) is definitely
what you'd want.

Maybe we should take a step back and ask ourselves: 
*why* is the bursty behaviour a problem for you?
Could you elaborate?

Best regards,
Marcus

On Sun, 2018-03-04 at 19:46 -0500, Jeff Long wrote:
> 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
> > com
> >         <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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