#15 - Add Spark socket wire benchmark notes

[cliffburdick]

This PR documents how to run Linux networking loopback tests (RDMA/Sockets) on the DGX Spark platform. Without configuring the system like this the benchmarks are not realistic since the traffic is looped through Linux rather than leaving on the wire.

[greptile-apps]

Greptile Summary

This PR adds a new SPARK_SOCKET_WIRE_README.md documenting how to configure Linux network namespaces and verify PHY-level counters for realistic DAQIRI socket benchmarks on a DGX Spark machine, alongside three small companion fixes to the socket manager.

• Documentation: step-by-step namespace setup, PHY-counter verification with ethtool -S, verified benchmark results table, and a restore-networking script for the tested enp1s0f0np0 → enp1s0f1np1 wire pair.
• UDP size cap: send_udp_burst now rejects any packet exceeding kMaxUdpPayloadBytes (65507) before calling sendmmsg; the burst is still freed unconditionally in send_tx_burst.
• TCP dead-connection guards: send_tx_burst adds conn->running.load() to its null check, and socket_connect_to_server short-circuits with the existing connection only after confirming running.load() is true.

Confidence Score: 5/5

Safe to merge; the code changes are small, targeted, and all three logic paths preserve the burst-free contract.

The UDP size check is a pure validation gate that fires before any I/O and leaves the burst lifecycle untouched. The conn->running.load() additions close the window where a TX call could race against a just-exited RX thread. The connection-reuse path in socket_connect_to_server correctly checks liveness before short-circuiting. No new invariants are broken and no new data paths are introduced.

No files require special attention.

Important Files Changed

Filename	Overview
SPARK_SOCKET_WIRE_README.md	New documentation file describing Linux namespace setup and PHY-counter verification for Spark socket wire benchmarks; no code logic changes.
src/managers/socket/daqiri_socket_mgr.cpp	Three focused fixes: UDP payload size cap at 65507 bytes, dead-connection guard added to send_tx_burst TCP path (conn->running.load()), and TCP connection reuse with live-state check in socket_connect_to_server; removal of self-erase from tcp_rx_loop is compensated by the reuse guard. Burst is freed unconditionally at end of send_tx_burst even when validation short-circuits.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[send_tx_burst] --> B{protocol?}
    B -- UDP --> C[send_udp_burst]
    C --> D{any pkt_len > 65507?}
    D -- yes --> E[return false / CONNECT_FAILURE]
    D -- no --> F[sendmmsg loop]
    F --> G[update tx_pkts / tx_bytes]
    B -- TCP --> H{conn == null OR NOT running?}
    H -- yes --> I[CONNECT_FAILURE]
    H -- no --> J[send_tcp_burst]
    J --> G
    G --> K[free_all_packets + free_tx_burst]
    E --> K
    I --> K

    subgraph socket_connect_to_server
        L[primary_conn_id set AND IP/port match?] -- yes --> M{connections_ find + running.load?}
        M -- alive --> N[return existing conn_id]
        M -- dead or missing --> O[create_tcp_client_connection]
        L -- no --> O
    end

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_{Reviews (2): Last reviewed commit: "#15 - Guard TCP socket connection reuse" | Re-trigger Greptile}

[dleshchev]

looks like dead connections can be still an issue; also the .md file needs to be placed somewhere more appropriate.

[dleshchev]

should this file live in tutorials?

[dleshchev]

may be needs a note that this is device-specific?

[cliffburdick]

This tutorial is specific to spark if that's what you mean

[dleshchev]

probably need an issue for that

[cliffburdick]

Added into PR #114