Responding to martin's question: * Yes, I have a QSFP to 4x SFP breakout cable * The underflows happen even when using just one USRP (i.e. remove all references to the second one from the benchmark)
________________________________ From: Eugene Grayver <[email protected]> Sent: Monday, June 29, 2026 1:17 PM To: Peter Jiacheng Gu <[email protected]> Cc: usrp-users <[email protected]> Subject: Re: [USRP-users] Underflows on X440 TX I have not tried the X4_400 image because I need many channels at relatively low (50 MHz) bandwidth. This issue must be solved — I've been able to use older USRPs for TX at rates up to 200 Msps. There is no reason for the X440 to behave this way. ________________________________ From: Peter Jiacheng Gu <[email protected]> Sent: Monday, June 29, 2026 12:23 PM To: Eugene Grayver <[email protected]> Cc: usrp-users <[email protected]> Subject: [EXTERNAL] Re: [USRP-users] Underflows on X440 TX Do not open links or attachments unless you recognize the sender. If unsure, click the Report Phish button or forward the email to OPSEC. Hi Eugene, I also encountered this issue. I’m currently investigating the X4_400 image since it supports the replay block. Have you already tried this? Best, Peter Am 29.06.2026 um 21:02 schrieb Eugene Grayver <[email protected]>: 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 _______________________________________________ USRP-users mailing list -- [email protected] To unsubscribe send an email to [email protected]
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