[Cherry-Pick][Bug Fix]fix the bug for real size 0 in cudagraph (#3888)

* fix the bug for real size 0 in cudagraph

* fix cache_messager

---------

Co-authored-by: Jiang-Jia-Jun <163579578+Jiang-Jia-Jun@users.noreply.github.com>

fastdeploy/worker/gpu_model_runner.py

@@ -42,6 +42,7 @@ from fastdeploy.model_executor.layers.sample.meta_data import SamplingMetadata
 from fastdeploy.model_executor.layers.sample.sampler import Sampler, SpeculativeSampler
 from fastdeploy.model_executor.model_loader import get_model_loader
 from fastdeploy.platforms import current_platform
+from fastdeploy.utils import ceil_div
 
 if current_platform.is_iluvatar():
     from fastdeploy.model_executor.ops.iluvatar import set_value_by_flags_and_idx
@@ -588,17 +589,16 @@ class GPUModelRunner(ModelRunnerBase):
         """Set dummy prefill inputs to share_inputs"""
         # NOTE(gongshaotian): The maximum decoding length is equal to the expected decoded tokens plus the eos token
         max_dec_len = expected_decode_len + 1
-        full_length = min(
-            num_tokens // batch_size,
+        input_length = min(
+            ceil_div(num_tokens, batch_size),
             self.parallel_config.max_model_len - max_dec_len,
         )
 
         # NOTE(wanglongzhi): When the full length is too large, DeepEP's buffer size will not be enough to cause the result to appear nan.
         # TODO(wanglongzhi): Figure out the accurate buffer size of DeepEP.
         if self.fd_config.parallel_config.enable_expert_parallel:
-            full_length = min(full_length, 32)
+            input_length = min(input_length, 32)
 
-        input_length = int(full_length * self.cache_config.kv_cache_ratio)
         block_num = (
             input_length + self.cache_config.block_size - 1
         ) // self.cache_config.block_size + self.cache_config.enc_dec_block_num