tcpretrans.bt

#!/usr/bin/env bpftrace
// SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
// SPDX-License-Identifier: Apache-2.0
//
// TCP retransmissions (network backpressure indicator).
// High retransmit rates indicate network congestion or packet loss.
//
// Usage: sudo bpftrace tcpretrans.bt

tracepoint:tcp:tcp_retransmit_skb
{
    printf("%-8d %-16s %s:%d -> %s:%d state=%d\n",
        pid, comm,
        ntop(args.saddr), args.sport,
        ntop(args.daddr), args.dport,
        args.state);
    @retrans[ntop(args.daddr), args.dport] = count();
    @total = count();
}

interval:s:10
{
    printf("\n--- TCP Retransmissions (last 10s) ---\n");
    printf("Total: ");
    print(@total);
    print(@retrans);
    clear(@retrans);
    clear(@total);
}