[Benchmark] Add retry support to fix workload bias in multi-turn benchmark (#28493)

benchmarks/multi_turn/benchmark_serving_multi_turn.py

@@ -55,6 +55,7 @@ class ClientArgs(NamedTuple):
     verify_output: bool
     conversation_sampling: ConversationSampling
     request_rate: float
+    max_retries: int
 
 
 class RequestArgs(NamedTuple):
@@ -527,6 +528,25 @@ async def poisson_sleep(request_rate: float, verbose: bool = False) -> None:
     await asyncio.sleep(interval)
 
 
+async def exponential_backoff_sleep(
+    attempt_cnt: int,
+    base_rate: float = 1.0,
+    backoff_factor: float = 2.0,
+    jitter_fraction: float = 0.10,
+    verbose: bool = False,
+) -> None:
+    # Sleep with exponential backoff and jitter after a failed request.
+    backoff_delay = base_rate * (backoff_factor**attempt_cnt)
+    jittered_delay = backoff_delay * (
+        1 + np.random.uniform(-jitter_fraction, jitter_fraction)
+    )
+
+    if verbose:
+        logger.info(f"Backoff for {jittered_delay:.3f} seconds...")
+
+    await asyncio.sleep(jittered_delay)
+
+
 async def client_main(
     args: ClientArgs,
     req_args: RequestArgs,
@@ -655,59 +675,62 @@ async def client_main(
                 )
                 time_of_last_turn[conv_id] = curr_time_sec
 
-            success = True
-            try:
-                result = await send_turn(
-                    session,
-                    client_id,
-                    conv_id,
-                    messages,
-                    current_turn,
-                    tokenizer,
-                    req_args,
-                    args.print_content,
-                    args.verify_output,
-                )
-                if result is not None:
-                    result_queue.put(result)
-                else:
-                    # None means that the request failed,
-                    # and should not be added to the statistics.
-                    success = False
-                    num_failures += 1
-
-                    logger.warning(
-                        f"{Color.YELLOW}Client {client_id} - Request rejected during conversation ID {conv_id} (turn: {current_turn}){Color.RESET}"  # noqa: E501
+            success = False
+            for attempt_cnt in range(args.max_retries + 1):
+                try:
+                    exception = False
+                    result = await send_turn(
+                        session,
+                        client_id,
+                        conv_id,
+                        messages,
+                        current_turn,
+                        tokenizer,
+                        req_args,
+                        args.print_content,
+                        args.verify_output,
+                    )
+                    if result is not None:
+                        result_queue.put(result)
+                        success = True
+                        break
+                    else:
+                        logger.warning(
+                            f"{Color.YELLOW}Client {client_id} - Request rejected during conversation ID {conv_id} (turn: {current_turn}){Color.RESET}"  # noqa: E501
+                        )
+                except asyncio.exceptions.TimeoutError:
+                    exception = True
+                    logger.error(
+                        "%sClient %d - Timeout during conversation ID %s (turn: %d). "
+                        "Base timeout is %ss (set with --request-timeout-sec), but the "
+                        "effective timeout may be longer based on max_tokens. If this "
+                        "is unexpected, consider increasing the timeout or checking "
+                        "model performance.%s",
+                        Color.RED,
+                        client_id,
+                        conv_id,
+                        current_turn,
+                        req_args.timeout_sec,
+                        Color.RESET,
+                    )
+                except Exception:
+                    exception = True
+                    logger.exception(
+                        f"{Color.RED}Client {client_id} - Exception during conversation ID {conv_id} (turn: {current_turn}){Color.RESET}"  # noqa: E501
                     )
 
-                    # Remove the conversation (should not be used again)
-                    active_convs.pop(conv_id)
-
-            except asyncio.exceptions.TimeoutError:
-                num_failures += 1
-                logger.error(
-                    "%sClient %d - Timeout during conversation ID %s (turn: %d). "
-                    "Base timeout is %ss (set with --request-timeout-sec), but the "
-                    "effective timeout may be longer based on max_tokens. If this "
-                    "is unexpected, consider increasing the timeout or checking "
-                    "model performance.%s",
-                    Color.RED,
-                    client_id,
-                    conv_id,
-                    current_turn,
-                    req_args.timeout_sec,
-                    Color.RESET,
-                )
-                break  # Exit gracefully instead of raising an error
+                # Sleep before retry if not last attempt
+                if not success and attempt_cnt < args.max_retries:
+                    await exponential_backoff_sleep(attempt_cnt, verbose=args.verbose)
 
-            except Exception:
+            if not success:
                 num_failures += 1
-                logger.exception(
-                    f"{Color.RED}Client {client_id} - Exception during conversation ID {conv_id} (turn: {current_turn}){Color.RESET}"  # noqa: E501
-                )
-                break  # Exit gracefully instead of raising an error
+                # Remove the conversation (should not be used again)
+                active_convs.pop(conv_id)
+                if exception:
+                    break  # Exit gracefully instead of raising an error
 
-            if success:
+            else:
                 num_successes += 1
 
                 # Update the turns counter to include the LLM response
@@ -822,6 +845,7 @@ def get_client_config(
         verify_output=args.verify_output,
         conversation_sampling=args.conversation_sampling,
         request_rate=args.request_rate,
+        max_retries=args.max_retries,
     )
 
     if args.limit_min_tokens > 0 or args.limit_max_tokens > 0:
@@ -1357,6 +1381,16 @@ async def main() -> None:
         help="Expected request rate (Poisson process) per client in requests/sec."
         "Set to 0 for no delay between requests.",
     )
+    parser.add_argument(
+        "--max-retries",
+        type=int,
+        default=int(os.environ.get("MULTITURN_BENCH_MAX_RETRIES", "0")),
+        help="Maximum number of retry attempts for timed-out requests. "
+        "Default is 0 (no retries). "
+        "Set to higher values to retry failed requests and maintain "
+        "fair workload distribution. "
+        "Can also be set via MULTITURN_BENCH_MAX_RETRIES environment variable.",
+    )
     parser.add_argument(
         "--conversation-sampling",
         type=ConversationSampling,