From ec8d498ba5040b7ba862211975d2043baa6e5536 Mon Sep 17 00:00:00 2001 From: Luke Hoersten Date: Mon, 15 Jun 2026 07:59:44 -0500 Subject: sdkconfig: revert TCP window bump — net-negative on /frame path MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Bumping WND/SND_BUF to 32 KiB + RECVMBOX to 16 + SACK on regressed ttfb from ~350µs to ~1.2ms across every frame and introduced periodic 250+ms body stalls (TCP retransmit on the larger window). Mean body unchanged. Reason: Scrypted's per-frame fetch() opens a fresh TCP socket, so the larger receive window just slows slow-start on every new connection rather than helping. Reverted to lwIP defaults. The real fix is HTTP keep-alive on the Scrypted side; will revisit window tuning once persistent connections are in place. README backlog updated with what we learned. --- README.md | 6 +++--- sdkconfig.defaults | 8 ++++++++ 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/README.md b/README.md index 64e0f6f..9af05e7 100644 --- a/README.md +++ b/README.md @@ -510,10 +510,10 @@ Network body is now ~85% of every frame; everything else is at or near hardware ### Current backlog, in rough priority order -1. **Network body shrink** — *the only remaining big lever*. The firmware is reading ~215 KB JPEGs at ~45 Mbit/s effective on a 100 Mbit Ethernet link — that's about 45% of theoretical. Two routes: - - **TCP tuning in `sdkconfig`**: bump `CONFIG_LWIP_TCP_WND_DEFAULT` and `CONFIG_LWIP_TCP_RCVMBOX_SIZE`, plus enable `CONFIG_LWIP_TCP_RTO_MIN` adjustments. With BDP at LAN-1 ms × 100 Mbit ≈ 12.5 KB, the default 5.7 KB window is half what we need; doubling it should add 30–50% throughput. +1. **Network body shrink** — *the only remaining big lever*. The firmware reads ~215 KB JPEGs at ~45 Mbit/s effective on a 100 Mbit Ethernet link (~45% of theoretical). Routes ranked by what we've actually tried: + - **HTTP keep-alive on the Scrypted side** (untried, recommended next). Currently Scrypted's `fetch` opens a fresh TCP socket per frame; the ~1 ms of slow-start at each connect is more impactful than the receive-window setting. - **Per-viewport JPEG quality** (`-q:v` on the ffmpeg side): -q:v 5 halves file size at modest visual cost. `body` halves with it. - Combined, total → ~22 ms → **~45 fps ceiling**. + - ~~TCP window tuning (`CONFIG_LWIP_TCP_WND_DEFAULT` etc.)~~ — *tried and reverted*. Bumping WND/SND_BUF to 32 KB regressed `ttfb` from ~350 µs to ~1.2 ms and added periodic 250 ms stalls. The per-frame fresh-socket pattern makes larger windows actually slow things down via slow-start. Revisit only after keep-alive lands. 2. **OTA firmware updates** — *low effort, gateway to fleet ops*. Partition table already has `ota_0` / `ota_1`. Add `esp_https_ota` (or a one-shot `POST /firmware` using `esp_ota_*`) so reflashing doesn't require USB. Critical once you have more than one viewport in production. 3. **Task watchdog + crash counters** — *low effort*. Enable the ESP-IDF task watchdog, surface its bite count in `/state` alongside the existing `decode_errors` / `state_post_failures`. Good hygiene. 4. **Multi-camera per viewport** — *medium effort*. Let one viewport listen to events from N cameras, picking which one to stream based on which fired. Useful for "show whichever doorbell rang" or zone monitoring. diff --git a/sdkconfig.defaults b/sdkconfig.defaults index 638f6e8..4c50a23 100644 --- a/sdkconfig.defaults +++ b/sdkconfig.defaults @@ -29,6 +29,14 @@ CONFIG_LWIP_IPV4=y CONFIG_LWIP_IPV6=y CONFIG_MDNS_MAX_INTERFACES=1 +# TCP receive-window tuning attempted (WND/SND_BUF=32k, RECVMBOX=16, +# SACK on). Measured net-negative on the /frame path: ttfb regressed +# from ~350µs to ~1.2ms, body unchanged, and periodic 250+ms stalls +# appeared. Reason: Scrypted's per-frame fetch() opens a fresh TCP +# socket each time, so the larger window just slows slow-start. +# Reverted; revisit once we switch to HTTP keep-alive on the Scrypted +# side. Keeping the lwIP defaults. + # HTTP server CONFIG_HTTPD_MAX_REQ_HDR_LEN=1024 CONFIG_HTTPD_MAX_URI_LEN=512 -- cgit v1.2.3