maskit opened a new pull request, #13554:
URL: https://github.com/apache/trafficserver/pull/13554
## Summary
Benchmarking qmux (HTTP/3-over-TCP) against H2 showed a throughput deficit
specific to large, single-stream responses, absent for small objects and
mostly recovered once multiple concurrent streams share a connection.
`QUICStream::send_data()` capped how much of one stream's data it sends
per write event to a fixed 16KB, regardless of contention. A large object
on a solo stream needs many separate event-loop round trips to drain,
each paying real per-event overhead (quiche iterator alloc/free, an FFI
crossing, a flush). This makes that per-event budget contention-aware:
it scales down toward the existing 16KB floor under real contention
(preserving today's fairness guarantee exactly), and grows toward a new
256KB ceiling when a stream has the connection's write path to itself.
The budget is sized from the writable-stream count observed during the
*previous* write event on that connection -- an intentional one-event-lag
tradeoff that avoids draining `quiche_conn_writable()` twice or
materializing a container just to count entries.
Also, while touching the HTTP/3 frame-handling path, removed some dead
code and per-request allocations found along the way:
- `Http3FrameDispatcher`'s per-type handler list moved from a
heap-allocated `std::vector` to fixed inline storage, since at most a
handful of handlers ever register per frame type and this dispatcher
is a per-transaction object.
- `Http3Transaction`'s five per-transaction helper objects (frame
generators/handlers) converted from heap-allocated pointers to value
members, removing five allocations/frees per HTTP/3 transaction.
- Removed `Http3UnknownFrame` and `Http3HeadersFrame`'s `ats_unique_buf`
constructor/factory overload, both fully dead code.
- Aligned `Http3HeadersFrame`'s send-path constructor to take
`IOBufferReader &` like `Http3DataFrame`'s equivalent, instead of `*`.
## Test plan
- [x] New unit test (`test_QUICStream.cc`) covers
`compute_fair_send_budget()`'s no-contention, heavy-contention,
mid-range, and floor-boundary cases.
- [x] `test_net` and `test_http3` pass against BoringSSL + quiche + qmux.
- [x] `test_net` and `test_http3` pass against OpenSSL's native QUIC
backend (a separate, non-quiche `NetVConnection` implementation
that also compiles this code).
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