diff --git a/python/sglang/srt/mem_cache/hiradix_cache.py b/python/sglang/srt/mem_cache/hiradix_cache.py
index 1fb6b9a7d..36e1eb721 100644
--- a/python/sglang/srt/mem_cache/hiradix_cache.py
+++ b/python/sglang/srt/mem_cache/hiradix_cache.py
@@ -5619,6 +5619,14 @@ class HiRadixCache(RadixCache):
         allocator = getattr(self.cache_controller, "cp_shared_l2_page_allocator", None)
         if allocator is None:
             return
+        if not getattr(self, "_placement_assert_warned", False):
+            self._placement_assert_warned = True
+            logger.warning(
+                "[CP-HiCache] SGLANG_CP_HICACHE_PLACEMENT_ASSERT is ON: every scheduler tick MIN/MAX-reduces "
+                "placement_digest across the CP group (2 blocking gloo collectives on the scheduler thread "
+                "BEFORE forward) + a SHA256 over the whole free-list. This is a DEBUG/bring-up invariant check "
+                "-- turn it OFF in production (unset the env) for the per-tick critical-path cost to vanish."
+            )
         local = int(allocator.placement_digest(), 16) % (1 << 61)
         lo = torch.tensor(local, dtype=torch.int64, device="cpu")
         hi = torch.tensor(local, dtype=torch.int64, device="cpu")