Hi Chad,Something that you can do to monitor the problem is to look in /proc/net/udp. This will show you the fill level of kernel UDP receive buffers. If you've set the buffer size to 32 MiB as recommended by the performance tuning tips, usually these sporadic drops are the result of the flowgraph consuming data at a rate slightly lower than the nominal sample rate for multiple seconds, rather than a brief but larger performance reduction. If this is the case, you can see how the buffer fill level slowly increases over the course of several seconds until the buffer fills up and packets are dropped. Looking at this won't solve your problem, but at least it will give you a way to monitor if you do some changes to try to improve the performance.
Best, Daniel. On 16/01/2025 19:38, Chad Spooner wrote:
All:I'm developing a comm system involving three SDRs: transmit, channel effects, and receiver.The channel SDR is controlled by a flowgraph that has various options for the channel: AWGN (h(\tau) = \delta(\tau)), LTI, and a couple time- variant frequency-selective channel models.I need to run the full three-SDR system over long periods of time to get stable average values for system-performance parameters.My problem is that the channel flowgraph reports underflows on the order of every hundred seconds or so (sometimes much less). I've tracked down these rare underflows in the channel to transient problems in the receiver flowgraph.So I put together a minimum flowgraph that shows the problem, which is attached. When I run it, I get output like this:[INFO] [UHD] linux; GNU C++ version 11.2.0; Boost_107400; UHD_4.1.0.5-3 [INFO] [X300] X300 initialization sequence... [INFO] [X300] Maximum frame size: 8000 bytes. [INFO] [X300] Radio 1x clock: 200 MHz usrp_source :info: set_min_output_buffer on block 1 to 2097152 usrp_sink :info: set_min_output_buffer on block 2 to 2097152 mmse_resampler_cc :info: set_min_output_buffer on block 4 to 2097152 fir_filter_blk<IN_T,OUT_T,TAP_T> :info: set_min_output_buffer on block 5 to 2097152 multiply_cc :info: set_min_output_buffer on block 9 to 2097152 sig_source :info: set_min_output_buffer on block 8 to 2097152 add_cc :info: set_min_output_buffer on block 6 to 2097152 fastnoise_source :info: set_min_output_buffer on block 7 to 2097152 *Uusrp_sink :error: In the last 579300 ms, 1 underflows occurred. Uusrp_sink :error: In the last 256008 ms, 1 underflows occurred. usrp_sink :error: In the last 84992 ms, 1 underflows occurred. UUusrp_sink :error: In the last 128008 ms, 1 underflows occurred.*The PSD of the filtered input signal appears correctly on a spectrum analyzer.System Information: 24-core Intel i9 system Ubuntu 22.04.5 LTS, kernel 5.19.0-46-generic #47~22.04.1-Ubuntu gnuradio 3.10.1.1 UHD 4.1.0.5-3I've taken some pains to optimize the OS settings for gnuradio/UHD along the lines suggested by the online tips athttps://kb.ettus.com/USRP_Host_Performance_Tuning_Tips_and_Tricks I've also tinkered with the minoutbuf parameter in the various blocks. Any advice? Thanks, Chad cyclostationary.blog cmspoo...@nwra.com -- Chad M. Spooner, PhD NorthWest Research Associates 149 Bonifacio Place, Suite 200 Monterey, CA 93940 cmspoo...@nwra.com 831 521 6743 NWRA Scientist/Engineer, VP, BoD cyclostationary.blog
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