diff --git a/benchmarks/benchmark_dataset.py b/benchmarks/benchmark_dataset.py
index 8671719bce72..55c0cf851264 100644
--- a/benchmarks/benchmark_dataset.py
+++ b/benchmarks/benchmark_dataset.py
@@ -349,8 +349,9 @@ def sample(
             # [1650, 939, 486] -> ['Ġcall', 'sh', 'ere']
             # To avoid uncontrolled change of the prompt length,
             # the encoded sequence is truncated before being decode again.
+            total_input_len = prefix_len + int(input_lens[i])
             re_encoded_sequence = tokenizer.encode(prompt, add_special_tokens=False)[
-                : input_lens[i]
+                :total_input_len
             ]
             prompt = tokenizer.decode(re_encoded_sequence)
             total_input_len = len(re_encoded_sequence)
diff --git a/examples/offline_inference/spec_decode.py b/examples/offline_inference/spec_decode.py
index eece8beced51..6fa68d2ecee1 100644
--- a/examples/offline_inference/spec_decode.py
+++ b/examples/offline_inference/spec_decode.py
@@ -39,6 +39,9 @@ def parse_args():
     parser.add_argument("--top-k", type=int, default=-1)
     parser.add_argument("--print-output", action="store_true")
     parser.add_argument("--output-len", type=int, default=256)
+    parser.add_argument("--model-dir", type=str, default=None)
+    parser.add_argument("--eagle-dir", type=str, default=None)
+    parser.add_argument("--max-model-len", type=int, default=2048)
     return parser.parse_args()
 
 
@@ -46,9 +49,10 @@ def main():
     args = parse_args()
     args.endpoint_type = "openai-chat"
 
-    model_dir = "meta-llama/Llama-3.1-8B-Instruct"
+    model_dir = args.model_dir
+    if args.model_dir is None:
+        model_dir = "meta-llama/Llama-3.1-8B-Instruct"
     tokenizer = AutoTokenizer.from_pretrained(model_dir)
-    max_model_len = 2048
 
     prompts = get_samples(args, tokenizer)
     # add_special_tokens is False to avoid adding bos twice when using chat templates
@@ -57,16 +61,18 @@ def main():
     ]
 
     if args.method == "eagle" or args.method == "eagle3":
-        if args.method == "eagle":
+        eagle_dir = args.eagle_dir
+        if args.method == "eagle" and eagle_dir is None:
             eagle_dir = "yuhuili/EAGLE-LLaMA3.1-Instruct-8B"
-        elif args.method == "eagle3":
+
+        elif args.method == "eagle3" and eagle_dir is None:
             eagle_dir = "yuhuili/EAGLE3-LLaMA3.1-Instruct-8B"
         speculative_config = {
             "method": args.method,
             "model": eagle_dir,
             "num_speculative_tokens": args.num_spec_tokens,
             "draft_tensor_parallel_size": args.draft_tp,
-            "max_model_len": max_model_len,
+            "max_model_len": args.max_model_len,
         }
     elif args.method == "ngram":
         speculative_config = {
@@ -74,7 +80,7 @@ def main():
             "num_speculative_tokens": args.num_spec_tokens,
             "prompt_lookup_max": args.prompt_lookup_max,
             "prompt_lookup_min": args.prompt_lookup_min,
-            "max_model_len": max_model_len,
+            "max_model_len": args.max_model_len,
         }
     else:
         raise ValueError(f"unknown method: {args.method}")
@@ -86,7 +92,7 @@ def main():
         enable_chunked_prefill=args.enable_chunked_prefill,
         max_num_batched_tokens=args.max_num_batched_tokens,
         enforce_eager=args.enforce_eager,
-        max_model_len=max_model_len,
+        max_model_len=args.max_model_len,
         max_num_seqs=args.max_num_seqs,
         gpu_memory_utilization=0.8,
         speculative_config=speculative_config,
diff --git a/vllm/benchmarks/datasets.py b/vllm/benchmarks/datasets.py
index 3efbe5695711..b3688d2340e4 100644
--- a/vllm/benchmarks/datasets.py
+++ b/vllm/benchmarks/datasets.py
@@ -320,6 +320,8 @@ def __init__(
         **kwargs,
     ) -> None:
         super().__init__(**kwargs)
+        random.seed(self.random_seed)
+        np.random.seed(self.random_seed)
 
     def sample(
         self,
@@ -376,10 +378,11 @@ def sample(
             # [1650, 939, 486] -> ['Ġcall', 'sh', 'ere']
             # To avoid uncontrolled change of the prompt length,
             # the encoded sequence is truncated before being decode again.
+            total_input_len = prefix_len + int(input_lens[i])
             re_encoded_sequence = tokenizer.encode(
-                prompt, add_special_tokens=False)[:input_lens[i]]
+                prompt, add_special_tokens=False)[:total_input_len]
             prompt = tokenizer.decode(re_encoded_sequence)
-            total_input_len = prefix_len + int(input_lens[i])
+            total_input_len = len(re_encoded_sequence)
             requests.append(
                 SampleRequest(
                     prompt=prompt,
@@ -692,7 +695,8 @@ def get_samples(args, tokenizer) -> list[SampleRequest]:
                                     dataset_path=args.dataset_path).
             sample(tokenizer=tokenizer, num_requests=args.num_prompts),
             "random":
-            lambda: RandomDataset(dataset_path=args.dataset_path).sample(
+            lambda: RandomDataset(random_seed=args.seed,
+                                  dataset_path=args.dataset_path).sample(
                 tokenizer=tokenizer,
                 num_requests=args.num_prompts,
                 prefix_len=args.random_prefix_len,
diff --git a/vllm/benchmarks/serve.py b/vllm/benchmarks/serve.py
index 302f655f424a..419284cca042 100644
--- a/vllm/benchmarks/serve.py
+++ b/vllm/benchmarks/serve.py
@@ -631,6 +631,12 @@ def add_cli_args(parser: argparse.ArgumentParser):
         help="The label (prefix) of the benchmark results. If not specified, "
         "the endpoint type will be used as the label.",
     )
+    parser.add_argument(
+        "--backend",
+        type=str,
+        default="vllm",
+        choices=list(ASYNC_REQUEST_FUNCS.keys()),
+    )
     parser.add_argument(
         "--base-url",
         type=str,