Important info up front: Hardware: USRP B210 Driver: Version: [INFO] [UHD] linux; GNU C++ version 4.8.5 20150623 (Red Hat 4.8.5-16); Boost_106700; UHD_3.11.1
I have an application that receives and transmits at the same time. The application receives a stream of data, does some simple processing, and transmits a response. I have three separate threads: one that gets data from the rx_streamer and writes to an Rx buffer, one that processes data from the Rx buffer and writes a response to a Tx buffer, and one that reads data from the Tx buffer and writes to a tx_streamer. The Rx and Tx streams are started using timed commands such that the Rx stream leads the Tx stream by 1 millisecond. The blocksize I'm using for Rx and Tx is much less than 1 millisecond and is determined by rx_streamer->get_max_num_samps(). I've profiled the processing routine, and it's about 20x faster than my rx_streamer sample rate, so I'm confident I'm able to keep up with the incoming data rate in the processing thread. I'm running into an issue which is causing underflows. *Every once and a while, my call to rx_streamer->recv() stalls for a bit, sometimes for 3-5 milliseconds.* The next several calls are very fast, like it's trying to catch up. I don't see any overflows on the Rx side. However, the initial stall delay is enough to starve my tx_streamer and cause underflows. Over time, my tx_streamer incurs a significant delay with respect to my rx_streamer. In order to further investigate the issue, I wrote a simple, single-threaded program that just starts an rx_stream and times the calls to recv(). I see the occasional stalls in this program as well. What could be causing these stalls, and are there any settings that might minimize them? My gut is telling me it's at the USB driver level and not at the UHD level. I've tried "renicing" the process to a high priority in case it's a scheduling issue, but that didn't seem to have any effect. Thanks for help, Daniel
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