Do not calculate presence or ephemeral events when they are filtered …

…out (#14970)

This expands the previous optimisation from being only for initial
sync to being for all sync requests.

It also inverts some of the logic to be inclusive instead of exclusive.

changelog.d/14970.misc

@@ -0,0 +1 @@
+Improve performance of `/sync` in a few situations.

synapse/handlers/sync.py

@@ -1459,10 +1459,12 @@ async def generate_sync_result(
             sync_result_builder, account_data_by_room
         )
 
-        block_all_presence_data = (
-            since_token is None and sync_config.filter_collection.blocks_all_presence()
+        # Presence data is included if the server has it enabled and not filtered out.
+        include_presence_data = (
+            self.hs_config.server.use_presence
+            and not sync_config.filter_collection.blocks_all_presence()
         )
-        if self.hs_config.server.use_presence and not block_all_presence_data:
+        if include_presence_data:
             logger.debug("Fetching presence data")
             await self._generate_sync_entry_for_presence(
                 sync_result_builder,
@@ -1841,15 +1843,12 @@ async def _generate_sync_entry_for_rooms(
         """
 
         since_token = sync_result_builder.since_token
-
-        # 1. Start by fetching all ephemeral events in rooms we've joined (if required).
         user_id = sync_result_builder.sync_config.user.to_string()
-        block_all_room_ephemeral = (
-            since_token is None
-            and sync_result_builder.sync_config.filter_collection.blocks_all_room_ephemeral()
-        )
 
-        if block_all_room_ephemeral:
+        # 1. Start by fetching all ephemeral events in rooms we've joined (if required).
+        if (
+            sync_result_builder.sync_config.filter_collection.blocks_all_room_ephemeral()
+        ):
             ephemeral_by_room: Dict[str, List[JsonDict]] = {}
         else:
             now_token, ephemeral_by_room = await self.ephemeral_by_room(