rust/wasmtime: set TCP_NODELAY on the connected socket - #45
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Latency-sensitive guests (QUIC over the message stream, per component-iroh) write small messages back-to-back; Nagle holds the second write until the peer's delayed ACK arrives, a ~40 ms stall per occurrence on Linux loopback. Browsers run WebSocket sockets with TCP_NODELAY, so the wasmtime host was the deficient implementation on the portability ladder (enhance, never accumulate divergence). Found driving component-iroh's endpoint to event-driven wakeups (polymorph-components/polymorph-iroh#42): with flushes no longer batched by a 10 ms clock tick, back-to-back small sends surfaced the stall — relay-wire echo roundtrips sat at 27-50 ms and drop to 0-7 ms with this change. Verified: just check; just conformance-ct (4 targets, 220 results, 0 failing).
lann
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With host-jco retired (#40), the portable workaround for its scheduler defect - bounded clock polling (5 ms method quantum / 10 ms pump tick) - protected nothing and cost ~5x handshake latency on every host. Wake-ups are now event-driven in both directions, riding wit-bindgen's inter-task-wakeup channel (both hosts deliver it): resource methods kick the pump to flush their mutations (first flight, stream writes, FIN/RESET/STOP_SENDING, datagrams, signals, closes, flow-control credit) and park on wakers in State::waiters; the pump wakes the waiters after every drain that progressed, on signal-inbox pushes, and unconditionally on its 10 ms tick, which stays for noq's timers and now also bounds deadline re-checks and any missed wake edge. The never-cancel-an-import teardown discipline is unchanged; the kick future is guest-local. Going event-driven exposed a latent Nagle stall in the websocket sibling's wasmtime host: back-to-back small sends (STREAM then FIN, no longer batched by the tick) sat out the peer's delayed ACK, putting relay-wire echo roundtrips at 27-50 ms. Fixed upstream (polymorph-components/polymorph-websocket#45, TCP_NODELAY); the websocket pin bumps to that commit here. The two changes are co-dependent: the pump change without the pin bump regresses relay roundtrips 23 -> ~47 ms. Bench on this machine (medians): endpoint handshakes 16/21/14 ms (relay/udp/webrtc) -> 1-4 ms, matching the spike; roundtrips 23/17/23 -> 0 ms; bulk throughput 7.7/49.1/38.1 -> 27.8/85.1/49.1 MB/s (prompt flow-control credit plus nodelay). The budgets tighten accordingly: absolute ceilings 2000 -> 250 ms, and the spike-to-endpoint handshake delta is asserted (<= 10 ms) so the polling tax cannot quietly return. Verified: just check, just probes (5/5), just matrix (12 pairings), just exam-deltic (5/5), just bench (budgets hold, handshake_tax_ms 0). Fixes #42
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Latency-sensitive guests (QUIC over the message stream, per component-iroh) write small messages back-to-back; Nagle holds the second write until the peer's delayed ACK arrives — a ~40 ms stall per occurrence on Linux loopback. Browsers run WebSocket sockets with TCP_NODELAY, so the wasmtime host is the deficient implementation on the portability ladder; this enhances it to match.
Found driving component-iroh's endpoint to event-driven wakeups (polymorph-components/polymorph-iroh#42): with guest flushes no longer batched by a 10 ms clock tick, back-to-back small sends surfaced the stall — relay-wire echo roundtrips sat at 27–50 ms and drop to 0–7 ms with this change (numbers from component-iroh's bench rig; its budget gate re-asserts them once its websocket pin bumps).
The
wss:(Rustls) arm is covered by reaching throughMaybeTlsStream::Rustls; the catch-all arm covers the enum's non-exhaustive future variants by leaving them as-is.Verified:
just check;just conformance-ct— 4 targets, 220 results, 0 failing.