Document Ornith 1.5 A/B benchmark

experiments/ornith15-ab/gpu_monitor.py

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+#!/usr/bin/env python3
+"""Sample physical GPU load during a GO-authorized A/B case."""
+import argparse
+import json
+import pathlib
+import subprocess
+import time
+
+
+def main():
+    p = argparse.ArgumentParser()
+    p.add_argument("--output", type=pathlib.Path, required=True)
+    p.add_argument("--interval", type=float, default=1.0)
+    p.add_argument("--go", action="store_true")
+    args = p.parse_args()
+    if not args.go:
+        p.error("No GPU monitoring before explicit --go")
+    args.output.parent.mkdir(parents=True, exist_ok=True)
+    cmd = ["nvidia-smi", "--query-gpu=uuid,name,memory.used,utilization.gpu,power.draw",
+           "--format=csv,noheader,nounits"]
+    with args.output.open("w") as out:
+        while True:
+            sample = subprocess.run(cmd, capture_output=True, text=True, timeout=15)
+            record = {"time": time.time(), "returncode": sample.returncode,
+                      "rows": [line.strip() for line in sample.stdout.splitlines() if line.strip()],
+                      "error": sample.stderr.strip() if sample.returncode else ""}
+            out.write(json.dumps(record) + "\n")
+            out.flush()
+            time.sleep(args.interval)
+
+
+if __name__ == "__main__":
+    main()