sahi-build-plugins

name	sahi-build-plugins
description	Rebuild and test the SAHI C++ plugins / nvinfer parser after editing them. Use when changing gst-nvsahipreprocess, gst-nvsahipostprocess, or libs/nvdsinfer_yolo, and you need to verify it compiles and the result is correct.

Build & test the SAHI plugins

There is no host build — the plugins need the DeepStream SDK headers, so build inside the container.

Build (fast path)

docker exec ds-sahi bash -lc 'cd /apps/deepstream-sahi && ./install.sh --plugins-only'

• --plugins-only rebuilds only nvsahipreprocess, nvsahipostprocess, and libnvds_infer_yolo.so (≈1–2 min). Flags -Wall -Werror -O2, so warnings fail the build.
• Outputs: /opt/nvidia/deepstream/deepstream/lib/gst-plugins/libnvdsgst_sahi{pre,post}process.so, /opt/nvidia/deepstream/deepstream/lib/libnvds_infer_yolo.so.
• Verify a parser symbol is exported: nm -D .../libnvds_infer_yolo.so | grep NvDsInferYolo.

Correctness A/B (MANDATORY for postprocess/parser changes)

A perf change must NOT change detections. Compare obj/frame before vs after on a dense video:

# baseline (current committed version):
docker exec ds-sahi bash -lc '... python3 deepstream_test_sahi.py --model <m> --no-display --csv -i ../videos/aerial_crowding_01.mp4'
# -> read results/*.csv mean total_objects, then edit, rebuild --plugins-only, re-run, and the mean MUST match bit-for-bit.

To revert for the A/B: git stash push -- <file> → rebuild → run → git stash pop → rebuild.

A real example from this repo: the SahiSpatialGrid::query visited-stamp change was neutral (~23% faster postprocess, identical results); a companion cell_size=median change altered results and was rejected. Always isolate one change at a time when results move.

Profiling

• Postprocess time: GST_DEBUG=nvsahipostprocess:4 → avg X ms/frame.
• The GST latency tracer does not give per-element times for DeepStream elements; instrument with a 1 s counter like the one in gstnvsahipostprocess.cpp if you need preprocess timing.

Gotchas

• results/ and built .so/.engine are root-owned (container) — sudo chown on the host if needed.
• Keep the container alive between edits so the engine cache + pyds build are reused.