bus-bench: decoder stand-in and mixed-load runs

Raw frames to four subscribers plus envelopes to five, at the car's rate and
at a full bus. Raw never suffered; envelope deliveries are the load, with the
knee near 40,000 deliveries/s.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

scripts/bus-bench.sh

@@ -6,12 +6,13 @@
 #   usage: bus-bench.sh BUS_BENCH_BINARY CAPTURE.log [secs]
 #   env:   BATCHES  batch windows in ms, 0 = one message per frame   ("0 10")
 #          FLAGS    extra options for both roles, e.g. --nagle
+#          SINKS    subscribers per run; each reports separately                 (1)
 #          GAP_MS   cangen gap for the full-bus run (0.15: ~4500 frames/s here, past what
 #                   500 kbit/s can carry with 8-byte frames)
 set -euo pipefail
 
 BIN="$1"; CAPTURE="$2"; SECS="${3:-20}"
-BATCHES="${BATCHES:-0 10}"; FLAGS="${FLAGS:-}"
+BATCHES="${BATCHES:-0 10}"; FLAGS="${FLAGS:-}"; SINKS="${SINKS:-1}"
 
 if ! ip link show vcan0 >/dev/null 2>&1; then
   sudo modprobe vcan
@@ -26,9 +27,12 @@ OUT=$(mktemp -d)
 # run NAME BATCH_MS GENERATOR...: the generator feeds vcan0 for a little over SECS seconds.
 run() {
   local name="$1" batch="$2"; shift 2
-  # shellcheck disable=SC2086
-  "$BIN" sink --secs "$SECS" $FLAGS > "$OUT/sink" 2>/dev/null &
-  local sink=$!
+  local sinks=() i
+  for i in $(seq "$SINKS"); do
+    # shellcheck disable=SC2086
+    "$BIN" sink --secs "$SECS" $FLAGS > "$OUT/sink$i" 2>/dev/null &
+    sinks+=($!)
+  done
   sleep 0.5
   # shellcheck disable=SC2086
   "$BIN" bridge --batch-ms "$batch" --secs $((SECS + 3)) $FLAGS > "$OUT/bridge" 2>/dev/null &
@@ -38,15 +42,15 @@ run() {
   broker=$(pgrep -x mosquitto); m0=$(ticks "$broker"); t0=$(date +%s.%N)
   timeout "$((SECS + 1))" "$@" >/dev/null 2>&1 || true
   m1=$(ticks "$broker"); t1=$(date +%s.%N)
-  wait "$sink" "$bridge"
+  wait "${sinks[@]}" "$bridge"
   python3 - "$name" "$batch" "$FLAGS" "$OUT" "$((m1 - m0))" "$HZ" "$t0" "$t1" <<'PY'
-import json, sys
+import glob, json, sys
 name, batch, flags, out, ticks, hz, t0, t1 = sys.argv[1:]
 r = {"run": name, "batch_ms": int(batch), "flags": flags,
-     "sink": json.load(open(f"{out}/sink")), "bridge": json.load(open(f"{out}/bridge")),
+     "sinks": [json.load(open(p)) for p in sorted(glob.glob(f"{out}/sink*"))], "bridge": json.load(open(f"{out}/bridge")),
      "mosquitto_cpu_pct": round(100 * int(ticks) / int(hz) / (float(t1) - float(t0)), 1)}
-for k in ("role",):
-    r["sink"].pop(k); r["bridge"].pop(k)
+for d in r["sinks"] + [r["bridge"]]:
+    d.pop("role")
 print(json.dumps(r))
 PY
 }