Performance optimizations inspired by lxin/quic kernel QUIC#13
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Performance optimizations inspired by lxin/quic kernel QUIC#13
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Inspired by lxin/quic kernel pnspace.c: O(1) duplicate detection via bit test instead of O(n) range scan. Fixed 4096-bit sliding window (512 bytes, zero heap allocation) replaces heap-allocated ArrayList. - PacketNumberBitmap: mark/contains O(1), getRanges scans for ACK gen - ReceivedPacketTracker no longer needs allocator for packet tracking - removeBelow shifts bitmap forward for ACK-of-ACK pruning - Window auto-shifts on large PN jumps (3/4 history preserved)
Detects RTT increases during slow start before actual packet loss, reducing bufferbloat on the first congestion event. - Standard → CSS transition on RTT increase above eta threshold - CSS grows by MSS/4 per ACK (vs MSS in standard slow start) - CSS exits to congestion avoidance after 5 consecutive rounds - CSS returns to standard if RTT stabilizes - Round tracking via largest_sent_pn boundary - Connection passes latest_rtt and largest_sent_pn to CC on ACK
When the pacer requests a delay < 1ms, sleep inline in the send loop instead of returning to the event loop (which has only ms-resolution timers). This gives ~microsecond pacing precision for high-throughput transfers, similar to the Linux kernel QUIC's hrtimer approach. Applied to both Server and Client event loops.
For the common case where stream data arrives in order (offset == read_pos and no buffered chunks), stores data in a fixed 1500-byte inline buffer instead of going through the AutoArrayHashMap. This eliminates hash map insert/lookup/orderedRemove operations on the hot path. Inspired by lxin/quic kernel's approach of minimizing per-frame allocation. The pop() path still returns heap-allocated data for caller ownership compatibility, but the push() path saves hash map overhead.
Two optimizations for the stream frame reassembly hot path: 1. Inline buffer: when data arrives in-order (offset == read_pos) and no out-of-order chunks are buffered, copy to a fixed 1500-byte inline buffer instead of going through AutoArrayHashMap operations. Avoids hash map insert on push for the common case. 2. swapRemove instead of orderedRemove in pop(): O(1) instead of O(n) for removing consumed chunks from the hash map. Order doesn't matter since lookup is by key (offset), not position.
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Summary
Performance optimizations inspired by the Linux kernel QUIC implementation (
lxin/quic). All changes are backwards-compatible, all 460 tests pass, and Go ↔ Zig WebTransport interop verified in both directions.pnspace.c.Thread.sleep()for pacer delays < 1ms in the send loop, bypassing the event loop's ms-only timer resolution. Similar to kernel'shrtimerapproach for pacing.orderedRemove(O(n)) withswapRemove(O(1)) since chunk map order is irrelevant for keyed lookup.Test plan
zig build test)zig build -Doptimize=ReleaseFast)