[perf] optimizations for sky jobs launch (#4341)

* cache AWS get_user_identities

With SSO enabled (and maybe without?) this takes about a second. We already use
an lru_cache for Azure, do the same here.

* skip optimization for sky jobs launch --yes

The only reason we call optimize for jobs_launch is to give a preview of the
resources we expect to use, and give the user an opportunity to back out if it's
not what they expect. If you use --yes or -y, you don't have a chance to back
out and you're probably running from a script, where you don't care.
Optimization can take ~2 seconds, so just skip it.

* update logging

* address PR comments

Author: cg505

sky/cli.py

@@ -3699,13 +3699,24 @@ def jobs_launch(
     dag_utils.maybe_infer_and_fill_dag_and_task_names(dag)
     dag_utils.fill_default_config_in_dag_for_job_launch(dag)
 
-    click.secho(f'Managed job {dag.name!r} will be launched on (estimated):',
-                fg='cyan')
     dag, _ = admin_policy_utils.apply(
         dag, use_mutated_config_in_current_request=False)
-    dag = sky.optimize(dag)
 
-    if not yes:
+    if yes:
+        # Skip resource preview if -y is set, since we are probably running in
+        # a script and the user won't have a chance to review it anyway.
+        # This can save a couple of seconds.
+        click.secho(
+            f'Resources for managed job {dag.name!r} will be computed on the '
+            'managed jobs controller, since --yes is set.',
+            fg='cyan')
+
+    else:
+        click.secho(
+            f'Managed job {dag.name!r} will be launched on (estimated):',
+            fg='cyan')
+        dag = sky.optimize(dag)
+
         prompt = f'Launching a managed job {dag.name!r}. Proceed?'
         if prompt is not None:
             click.confirm(prompt, default=True, abort=True, show_default=True)

sky/clouds/aws.py

@@ -663,6 +663,7 @@ def _is_access_key_of_type(type_str: str) -> bool:
             return AWSIdentityType.SHARED_CREDENTIALS_FILE
 
     @classmethod
+    @functools.lru_cache(maxsize=1)  # Cache since getting identity is slow.
     def get_user_identities(cls) -> Optional[List[List[str]]]:
         """Returns a [UserId, Account] list that uniquely identifies the user.
 

sky/execution.py

@@ -267,6 +267,12 @@ def _execute(
                     # no-credential machine should not enter optimize(), which
                     # would directly error out ('No cloud is enabled...').  Fix
                     # by moving `sky check` checks out of optimize()?
+
+                    controller = controller_utils.Controllers.from_name(
+                        cluster_name)
+                    if controller is not None:
+                        logger.info(
+                            f'Choosing resources for {controller.name}...')
                     dag = sky.optimize(dag, minimize=optimize_target)
                     task = dag.tasks[0]  # Keep: dag may have been deep-copied.
                     assert task.best_resources is not None, task