[thweetkomputer]

Adaptive mode can currently turn into polling when a PMD rejects RX interrupts or a queue cannot provide a usable notification descriptor. On a 16-worker Azure NetVSC run this made an idle adaptive server consume 16 CPUs while reporting per-queue fallback messages.

This change keeps both poll and adaptive, including the existing default. Adaptive startup validates every hardware RX queue and fails with an explicit BYCORF_DPDK_MODE=poll suggestion if notifications are unavailable. Notification registration and interrupt failures during execution terminate the server instead of silently spinning; peers are stopped before the all-worker teardown barriers.

The mlx5 PMD acknowledges RDMA event-channel records itself. Its empty-channel EAGAIN on interrupt disable is valid after startup probes or timer/mailbox wakes, and is not treated as unsupported hardware. TAP packet descriptors and mlx5 event channels are not read as ordinary eventfds.

Validation on Ubuntu 24.04, GCC 13, Release, DPDK/SPDK enabled:

• Link-time fault injection with the ring PMD covers configuration rejection without a retry, missing notification descriptors, interrupt enable/disable rejection, runtime enable/disable failure with two workers, explicit poll startup, and mlx5 empty-channel handling.
• TAP smoke covers both modes, 100 streams, half-close, 80 idle wakeups, cross-worker RX/TX forwarding, and shutdown with open sockets.
• Lavik runtime-backend smoke covers data, recovery, kernel/DPDK switches, and clean shutdown.
• Formatting uses clang-format 23.1.1; git diff --check passes.

Runtime and networking architecture documentation and the mode configuration guide are updated. On the Azure ConnectX-5 VF (mlx5_pci), 16 adaptive workers and 16 RX/TX queues start successfully, recover a six-device SPDK dataset with one billion keys, and answer remote PING/DBSIZE. After recovery, idle process CPU averages 11.4% of one CPU (0.114 CPU) across five one-second samples; the previous NetVSC fallback consumed about 16 CPUs. These are idle-mode checks, not throughput results.

[coderabbitai]

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