only use concurrency when tasks have tags (#14781)

src/prefect/task_engine.py

@@ -785,7 +785,10 @@ def call_task_fn(
         if transaction.is_committed():
             result = transaction.read()
         else:
-            if PREFECT_EXPERIMENTAL_ENABLE_CLIENT_SIDE_TASK_ORCHESTRATION.value():
+            if (
+                PREFECT_EXPERIMENTAL_ENABLE_CLIENT_SIDE_TASK_ORCHESTRATION.value()
+                and self.task.tags
+            ):
                 # Acquire a concurrency slot for each tag, but only if a limit
                 # matching the tag already exists.
                 with concurrency(
@@ -1328,7 +1331,10 @@ async def call_task_fn(
         if transaction.is_committed():
             result = transaction.read()
         else:
-            if PREFECT_EXPERIMENTAL_ENABLE_CLIENT_SIDE_TASK_ORCHESTRATION.value():
+            if (
+                PREFECT_EXPERIMENTAL_ENABLE_CLIENT_SIDE_TASK_ORCHESTRATION.value()
+                and self.task.tags
+            ):
                 # Acquire a concurrency slot for each tag, but only if a limit
                 # matching the tag already exists.
                 async with aconcurrency(

tests/test_task_engine.py

@@ -2306,6 +2306,42 @@ def bar():
                 else:
                     assert acquire_spy.call_count == 0
 
+    async def test_no_tags_no_concurrency(self):
+        @task
+        async def bar():
+            return 42
+
+        with mock.patch(
+            "prefect.concurrency.asyncio._acquire_concurrency_slots",
+            wraps=_acquire_concurrency_slots,
+        ) as acquire_spy:
+            with mock.patch(
+                "prefect.concurrency.asyncio._release_concurrency_slots",
+                wraps=_release_concurrency_slots,
+            ) as release_spy:
+                await bar()
+
+                assert acquire_spy.call_count == 0
+                assert release_spy.call_count == 0
+
+    def test_no_tags_no_concurrency_sync(self):
+        @task
+        def bar():
+            return 42
+
+        with mock.patch(
+            "prefect.concurrency.sync._acquire_concurrency_slots",
+            wraps=_acquire_concurrency_slots,
+        ) as acquire_spy:
+            with mock.patch(
+                "prefect.concurrency.sync._release_concurrency_slots",
+                wraps=_release_concurrency_slots,
+            ) as release_spy:
+                bar()
+
+                assert acquire_spy.call_count == 0
+                assert release_spy.call_count == 0
+
     async def test_tag_concurrency_does_not_create_limits(
         self, enable_client_side_task_run_orchestration, prefect_client
     ):