Hi Eugene, Thanks for sharing this. I agree, this is unexpected. You describe that you’re using two X440s and this is also what you do in your benchmark_rate command, even though only the channels of the first device are in use. What’s the behavior if you omit everything about the second device, so basically only use ./benchmark_rate --args=addr=192.168.10.2,second_addr=192.168.11.2,mgmt_addr=192.168.1.10,clock_source=external,use_dpdk=1,type=x4xx,product=x440 --tx_channels 0,1,2,3,4,5,6,7 --tx_rate 40.96e6 --tx_cpu sc16 --multi_streamer --duration 120
Does that show the same underflow behavior (that would make it easier to reproduce)? You describe that you use two 10 GbE direct connect cables for each USRP. Does that mean you have a breakout cable and use two lanes of that from each USRP? /Martin From: Eugene Grayver <[email protected]> Sent: Monday, June 29, 2026 9:02 PM To: usrp-users <[email protected]> Subject: [EXTERNAL] [USRP-users] Underflows on X440 TX Hello, I am returning to the problem reported a few months ago: I have two X440s with X_200 image connected to a Threadripper 24 core. I am using two 10 GbE direct connect cables for each USRP (total of 4x 10 GbE). I was able to get RX working, but TX is getting continuous underflows. * Using the benchark_rate example. * Underflows observed both w/ DPDK and w/out DPDK * Underflows observed with 4, 8 channels and 16 channels * Fewer underflows with 4 channels, but still get a few per minute * Priority high/normal does not make a difference (usually) IMPORTANT: If I use only one interface ( —args=addr=192.168.10.2,mgmt_addr=192.168.1.10) there are no underflows with up to 7 channels (max to fit in 10 GbE). ./benchmark_rate --args=addr0=192.168.10.2,second_addr0=192.168.11.2,mgmt_addr0=192.168.1.10,addr1=192.168.15.2,second_addr1=192.168.16.2,mgmt_addr1=192.168.1.20,clock_source=external,use_dpdk=1,type=x4xx,product=x440 --tx_channels 0,1,2,3,4,5,6,7 --tx_rate 40.96e6 --tx_cpu sc16 --multi_streamer --duration 120 This should be trivial for such a powerful machine! I am suspecting an issue with handling of packets across multiple network interfaces. Are the TX flow control packets not getting to the right place? This is a critical failure — not something I expect for a $35k box 🙂 Eugene Grayver, Ph.D. Principal Engineer 310-336-1274
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