Report native HTTP chunk timing

scripts/bench_episode_byte_cache.py

@@ -618,6 +618,8 @@ def _print_range_timing_summary(fetch_pool: dict[str, float]) -> None:
         ("range_header_s", "http response headers"),
         ("range_first_byte_s", "http first body byte"),
         ("range_body_s", "http body drain"),
+        ("range_chunk_gap_s", "http chunk wait"),
+        ("range_join_s", "join response chunks"),
         ("range_retry_sleep_s", "http retry sleep"),
     ):
         value = fetch_pool.get(key)
@@ -635,6 +637,14 @@ def _print_range_timing_summary(fetch_pool: dict[str, float]) -> None:
     if status_counts:
         summary = ", ".join(f"{status}={count:.0f}" for status, count in sorted(status_counts.items()))
         print(f"| http status counts | {summary} |")
+    chunks = fetch_pool.get("range_chunks", 0.0)
+    if chunks > 0:
+        bytes_read = fetch_pool.get("range_bytes", 0.0)
+        body_s = fetch_pool.get("range_body_s", 0.0)
+        print(f"| http chunks/range | {chunks / range_jobs:.1f} |")
+        print(f"| http avg KiB/chunk | {bytes_read / chunks / 1024:.1f} |")
+        if body_s > 0:
+            print(f"| http body MiB/s | {bytes_read / body_s / 1024**2:.1f} |")
     print(f"| range reads | {range_jobs:.0f} |")
     print(f"| avg MiB/range | {fetch_pool.get('range_bytes', 0.0) / range_jobs / 1024**2:.1f} |")
 

src/lerobot/datasets/episode_video_streaming.py

@@ -387,20 +387,32 @@ class NativeHTTPRangeFetcher:
             chunks = []
             first_byte_s = 0.0
             first_chunk = True
-            body_start = time.perf_counter()
+            chunk_gap_s = 0.0
+            chunk_count = 0.0
+            previous_chunk_at = body_start = time.perf_counter()
             for chunk in response.iter_bytes():
+                now = time.perf_counter()
                 if first_chunk:
-                    first_byte_s = time.perf_counter() - body_start
+                    first_byte_s = now - body_start
                     first_chunk = False
+                chunk_gap_s += now - previous_chunk_at
+                previous_chunk_at = now
+                chunk_count += 1.0
                 chunks.append(chunk)
             body_s = time.perf_counter() - body_start
+            join_start = time.perf_counter()
+            payload = b"".join(chunks)
+            join_s = time.perf_counter() - join_start
             return (
-                b"".join(chunks),
+                payload,
                 response.status_code,
                 {
                     "range_header_s": header_s,
                     "range_first_byte_s": first_byte_s,
                     "range_body_s": body_s,
+                    "range_join_s": join_s,
+                    "range_chunks": chunk_count,
+                    "range_chunk_gap_s": chunk_gap_s,
                 },
             )