[Scheduler] Add configurable decode interval after prefill (#35017)

python/sglang/srt/server_args.py

@@ -804,6 +804,11 @@ class ServerArgs:
         "The maximum number of tokens in a chunk for the chunked prefill. Setting this to -1 means disabling chunked prefill.",
         NS("schedule"),
     ] = None
+    prefill_decode_interval: A[
+        int,
+        "The number of decode rounds to run after a prefill batch before scheduling the next prefill. In data-parallel attention mode, the interval is synchronized across all DP ranks. Set to 0 to disable.",
+        NS("schedule"),
+    ] = 0
     enable_dynamic_chunking: A[
         bool,
         "Enable dynamic chunk size adjustment for pipeline parallelism. When enabled, chunk sizes are dynamically calculated based on fitted function to maintain consistent execution time across chunks.",
@@ -3640,6 +3645,7 @@ class ServerArgs:
         self._handle_return_hidden_states_mode()
         self._handle_media_url_security()
         self._handle_hicache_ratio_default()
+        self._validate_prefill_decode_interval()
         if self.model_path.lower() in ["none", "dummy"]:
             return
 
@@ -8690,6 +8696,10 @@ class ServerArgs:
                 f"(got {self.asr_max_concurrent_sessions})."
             )
 
+    def _validate_prefill_decode_interval(self):
+        if self.prefill_decode_interval < 0:
+            raise ValueError("--prefill-decode-interval must be non-negative.")
+
     def _handle_other_validations(self):
         if self.default_chat_template_kwargs is not None and not isinstance(
             self.default_chat_template_kwargs, dict