[HiCache][PD] fix: keep decode load-back polling out of rank-local collectives

python/sglang/srt/disaggregation/decode_hicache_mixin.py

@@ -288,13 +288,8 @@ def _process_hicache_local_restores(self, decode_reqs: List[DecodeRequest]) -> N
             ):
                 dr.hicache_restore_status = HiCacheRestoreResult.READY
 
-        # Phase B: queue new load_back ops if the next slot is free.
-        # The (producer_index + 1) check ensures we never overwrite a still-in-flight slot:
-        # if a previous req holds that slot and isn't done, its event won't be signaled.
-        counter = self.tree_cache.cache_controller.layer_done_counter
-        if not self.tree_cache.is_load_back_event_done(
-            (counter.producer_index + 1) % counter.num_counters
-        ):
+        # Phase B: queue new load_back ops if the next slot is free on every rank.
+        if not self.tree_cache.has_free_load_back_slot():
             return
         queued = [
             dr

python/sglang/srt/mem_cache/unified_radix_cache.py

@@ -3523,25 +3523,19 @@ def ready_to_load_host_cache(self) -> int:
         return 0
 
     def is_load_back_event_done(self, consumer_index: int) -> bool:
-        """Return True after the local load-back event is complete.
-
-        Lets the disagg decode restore state machine
-        (``DecodeHiCacheTransferMixin``) gate on load-back completion; the
-        controller-level ``layer_done_counter`` event is shared across cache
-        implementations, while the tree-side bookkeeping runs in
-        ``loading_check``.
-        """
+        """Return True after this rank's load-back event is complete."""
         if consumer_index < 0 or self.cache_controller is None:
             return True
 
         finish_event = self.cache_controller.layer_done_counter.events[
             consumer_index
         ].finish_event
-        if not finish_event.query():
-            return False
+        return finish_event.query()
 
-        self.loading_check()
-        return True
+    def has_free_load_back_slot(self) -> bool:
+        """Acks are reaped in lockstep, so every rank agrees on this."""
+        cc = self.cache_controller
+        return len(cc.ack_load_queue) < cc.layer_done_counter.num_counters
 
     # ---- Query / Inspection APIs ----
     # These APIs exist for compatibility with other RadixTree implementations.