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--></style></head><body lang=EN-US link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt'>Another weird fact is that </span><span style='font-size:11.0pt'>rx_mbuf_allocation_errors grows even after we stopped the traffic on the generator side.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Why the nic keeps saying “sorry, I could not allocate an mbuf for the incoming packet” if there are no incoming packets?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span style='font-size:11.0pt;mso-ligatures:none'>From:</span></b><span style='font-size:11.0pt;mso-ligatures:none'> Ernesto Ruffini <eruffini@outsys.org> <br><b>Sent:</b> Tuesday, January 27, 2026 10:44<br><b>To:</b> users@dpdk.org<br><b>Subject:</b> ICE driver blocks<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-size:11.0pt'>Hi,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>We are using DPDK 25.11 with an Intel E810 with Firmware 4.90 and comms DDP 1.3.55 configured 8x10G<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>We generate traffic and direct it to one of the server’s nics, which is configured to forward it back to the generator via l2fwd:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Courier New"'>./build/l2fwd -l 14,16 -a 0000:4b:00.4 -a 0000:4b:00.5 -- -p 0x3 -P<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Everything works fine if we leave all defaults.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Problems arise when we diminish the number of mbufs: l2fwd has a nice formula to compute it:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> </span><span style='font-size:11.0pt;font-family:"Courier New"'>nb_mbufs = RTE_MAX(nb_ports * (nb_rxd + nb_txd + MAX_PKT_BURST + nb_lcores * MEMPOOL_CACHE_SIZE), 8192U);<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>(in our example, this amounts to 8192)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>If we then divide this by 4:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'> </span><span style='font-size:11.0pt;font-family:"Courier New"'>nb_mbufs /= 4;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>recompile and run it again, the effect is that only 2k packets are forwarded, then everything blocks, as seen in the l2fwd output: the number of “Total packets sent” remains at 2032.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Using dpdk-telemetry we see that "rx_mbuf_allocation_errors" counter grows indefinitely.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>In our understanding, diminishing the number of mbufs could degrade performance but not block the forwarding, as mbufs would eventually be freed by the nic once the packets are sent. And in fact this is the behavior we see using mlx5 driver for example.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Are we missing some specific configuration? Or is it an unexpected behavior?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'>Thanks<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt'><o:p> </o:p></span></p></div></body></html>