Fix #6102

polkadot/runtime/parachains/src/assigner_coretime/mod.rs

@@ -236,17 +236,9 @@ pub mod pallet {
 	#[pallet::error]
 	pub enum Error<T> {
 		AssignmentsEmpty,
-		/// Assignments together exceeded 57600.
-		OverScheduled,
-		/// Assignments together less than 57600
-		UnderScheduled,
 		/// assign_core is only allowed to append new assignments at the end of already existing
-		/// ones.
+		/// ones or update the last entry.
 		DisallowedInsert,
-		/// Tried to insert a schedule for the same core and block number as an existing schedule
-		DuplicateInsert,
-		/// Tried to add an unsorted set of assignments
-		AssignmentsNotSorted,
 	}
 }
 
@@ -387,67 +379,56 @@ impl<T: Config> Pallet<T> {
 
 	/// Append another assignment for a core.
 	///
-	/// Important only appending is allowed. Meaning, all already existing assignments must have a
-	/// begin smaller than the one passed here. This restriction exists, because it makes the
-	/// insertion O(1) and the author could not think of a reason, why this restriction should be
-	/// causing any problems. Inserting arbitrarily causes a `DispatchError::DisallowedInsert`
-	/// error. This restriction could easily be lifted if need be and in fact an implementation is
-	/// available
-	/// [here](https://github.com/paritytech/polkadot-sdk/pull/1694/commits/c0c23b01fd2830910cde92c11960dad12cdff398#diff-0c85a46e448de79a5452395829986ee8747e17a857c27ab624304987d2dde8baR386).
-	/// The problem is that insertion complexity then depends on the size of the existing queue,
-	/// which makes determining weights hard and could lead to issues like overweight blocks (at
-	/// least in theory).
+	/// Important: Only appending is allowed or insertion into the last item. Meaning,
+	/// all already existing assignments must have a `begin` smaller or equal than the one passed
+	/// here.
+	/// Updating the last entry is supported to allow for making a core assignment multiple calls to
+	/// assign_core. Thus if you have too much interlacing for e.g. a single UMP message you can
+	/// split that up into multiple messages, each triggering a call to `assign_core`, together
+	/// forming the total assignment.
+	///
+	/// Inserting arbitrarily causes a `DispatchError::DisallowedInsert` error.
+	// With this restriction this function allows for O(1) complexity. It could easily be lifted, if
+	// need be and in fact an implementation is available
+	// [here](https://github.com/paritytech/polkadot-sdk/pull/1694/commits/c0c23b01fd2830910cde92c11960dad12cdff398#diff-0c85a46e448de79a5452395829986ee8747e17a857c27ab624304987d2dde8baR386).
+	// The problem is that insertion complexity then depends on the size of the existing queue,
+	// which makes determining weights hard and could lead to issues like overweight blocks (at
+	// least in theory).
 	pub fn assign_core(
 		core_idx: CoreIndex,
 		begin: BlockNumberFor<T>,
-		assignments: Vec<(CoreAssignment, PartsOf57600)>,
+		mut assignments: Vec<(CoreAssignment, PartsOf57600)>,
 		end_hint: Option<BlockNumberFor<T>>,
 	) -> Result<(), DispatchError> {
 		// There should be at least one assignment.
 		ensure!(!assignments.is_empty(), Error::<T>::AssignmentsEmpty);
 
-		// Checking for sort and unique manually, since we don't have access to iterator tools.
-		// This way of checking uniqueness only works since we also check sortedness.
-		assignments.iter().map(|x| &x.0).try_fold(None, |prev, cur| {
-			if prev.map_or(false, |p| p >= cur) {
-				Err(Error::<T>::AssignmentsNotSorted)
-			} else {
-				Ok(Some(cur))
-			}
-		})?;
-
-		// Check that the total parts between all assignments are equal to 57600
-		let parts_sum = assignments
-			.iter()
-			.map(|assignment| assignment.1)
-			.try_fold(PartsOf57600::ZERO, |sum, parts| {
-				sum.checked_add(parts).ok_or(Error::<T>::OverScheduled)
-			})?;
-		ensure!(parts_sum.is_full(), Error::<T>::UnderScheduled);
-
 		CoreDescriptors::<T>::mutate(core_idx, |core_descriptor| {
 			let new_queue = match core_descriptor.queue {
 				Some(queue) => {
-					ensure!(begin > queue.last, Error::<T>::DisallowedInsert);
-
-					CoreSchedules::<T>::try_mutate((queue.last, core_idx), |schedule| {
-						if let Some(schedule) = schedule.as_mut() {
-							debug_assert!(schedule.next_schedule.is_none(), "queue.end was supposed to be the end, so the next item must be `None`!");
-							schedule.next_schedule = Some(begin);
+					ensure!(begin >= queue.last, Error::<T>::DisallowedInsert);
+
+					// Update queue if we are appending:
+					if begin > queue.last {
+						CoreSchedules::<T>::mutate((queue.last, core_idx), |schedule| {
+							if let Some(schedule) = schedule.as_mut() {
+								debug_assert!(schedule.next_schedule.is_none(), "queue.end was supposed to be the end, so the next item must be `None`!");
+								schedule.next_schedule = Some(begin);
+							} else {
+								defensive!("Queue end entry does not exist?");
+							}
+						});
+					}
+
+					CoreSchedules::<T>::mutate((begin, core_idx), |schedule| {
+						let assignments = if let Some(mut old_schedule) = schedule.take() {
+							old_schedule.assignments.append(&mut assignments);
+							old_schedule.assignments
 						} else {
-							defensive!("Queue end entry does not exist?");
-						}
-						CoreSchedules::<T>::try_mutate((begin, core_idx), |schedule| {
-							// It should already be impossible to overwrite an existing schedule due
-							// to strictly increasing block number. But we check here for safety and
-							// in case the design changes.
-							ensure!(schedule.is_none(), Error::<T>::DuplicateInsert);
-							*schedule =
-								Some(Schedule { assignments, end_hint, next_schedule: None });
-							Ok::<(), DispatchError>(())
-						})?;
-						Ok::<(), DispatchError>(())
-					})?;
+							assignments
+						};
+						*schedule = Some(Schedule { assignments, end_hint, next_schedule: None });
+					});
 
 					QueueDescriptor { first: queue.first, last: begin }
 				},

polkadot/runtime/parachains/src/assigner_coretime/tests.rs

@@ -235,10 +235,7 @@ fn assign_core_works_with_prior_schedule() {
 }
 
 #[test]
-// Invariants: We assume that CoreSchedules is append only and consumed. In other words new
-// schedules inserted for a core must have a higher block number than all of the already existing
-// schedules.
-fn assign_core_enforces_higher_block_number() {
+fn assign_core_enforces_higher_or_equal_block_number() {
 	let core_idx = CoreIndex(0);
 
 	new_test_ext(GenesisConfigBuilder::default().build()).execute_with(|| {
@@ -255,7 +252,7 @@ fn assign_core_enforces_higher_block_number() {
 		assert_ok!(CoretimeAssigner::assign_core(
 			core_idx,
 			BlockNumberFor::<Test>::from(15u32),
-			default_test_assignments(),
+			vec![(CoreAssignment::Idle, PartsOf57600(28800))],
 			None,
 		));
 
@@ -281,32 +278,27 @@ fn assign_core_enforces_higher_block_number() {
 			),
 			Error::<Test>::DisallowedInsert
 		);
+		// Call assign core again on last entry should work:
+		assert_eq!(
+			CoretimeAssigner::assign_core(
+				core_idx,
+				BlockNumberFor::<Test>::from(15u32),
+				vec![(CoreAssignment::Pool, PartsOf57600(28800))],
+				None,
+			),
+			Ok(())
+		);
 	});
 }
 
 #[test]
 fn assign_core_enforces_well_formed_schedule() {
-	let para_id = ParaId::from(1u32);
 	let core_idx = CoreIndex(0);
 
 	new_test_ext(GenesisConfigBuilder::default().build()).execute_with(|| {
 		run_to_block(1, |n| if n == 1 { Some(Default::default()) } else { None });
 
 		let empty_assignments: Vec<(CoreAssignment, PartsOf57600)> = vec![];
-		let overscheduled = vec![
-			(CoreAssignment::Pool, PartsOf57600::FULL),
-			(CoreAssignment::Task(para_id.into()), PartsOf57600::FULL),
-		];
-		let underscheduled = vec![(CoreAssignment::Pool, PartsOf57600(30000))];
-		let not_unique = vec![
-			(CoreAssignment::Pool, PartsOf57600::FULL / 2),
-			(CoreAssignment::Pool, PartsOf57600::FULL / 2),
-		];
-		let not_sorted = vec![
-			(CoreAssignment::Task(para_id.into()), PartsOf57600(19200)),
-			(CoreAssignment::Pool, PartsOf57600(19200)),
-			(CoreAssignment::Idle, PartsOf57600(19200)),
-		];
 
 		// Attempting assign_core with malformed assignments such that all error cases
 		// are tested
@@ -319,42 +311,6 @@ fn assign_core_enforces_well_formed_schedule() {
 			),
 			Error::<Test>::AssignmentsEmpty
 		);
-		assert_noop!(
-			CoretimeAssigner::assign_core(
-				core_idx,
-				BlockNumberFor::<Test>::from(11u32),
-				overscheduled,
-				None,
-			),
-			Error::<Test>::OverScheduled
-		);
-		assert_noop!(
-			CoretimeAssigner::assign_core(
-				core_idx,
-				BlockNumberFor::<Test>::from(11u32),
-				underscheduled,
-				None,
-			),
-			Error::<Test>::UnderScheduled
-		);
-		assert_noop!(
-			CoretimeAssigner::assign_core(
-				core_idx,
-				BlockNumberFor::<Test>::from(11u32),
-				not_unique,
-				None,
-			),
-			Error::<Test>::AssignmentsNotSorted
-		);
-		assert_noop!(
-			CoretimeAssigner::assign_core(
-				core_idx,
-				BlockNumberFor::<Test>::from(11u32),
-				not_sorted,
-				None,
-			),
-			Error::<Test>::AssignmentsNotSorted
-		);
 	});
 }
 
@@ -374,7 +330,14 @@ fn next_schedule_always_points_to_next_work_plan_item() {
 			Schedule { next_schedule: Some(start_4), ..default_test_schedule() };
 		let expected_schedule_4 =
 			Schedule { next_schedule: Some(start_5), ..default_test_schedule() };
-		let expected_schedule_5 = default_test_schedule();
+		let expected_schedule_5 = Schedule {
+			next_schedule: None,
+			end_hint: None,
+			assignments: vec![
+				(CoreAssignment::Pool, PartsOf57600(28800)),
+				(CoreAssignment::Idle, PartsOf57600(28800)),
+			],
+		};
 
 		// Call assign_core for each of five schedules
 		assert_ok!(CoretimeAssigner::assign_core(
@@ -408,7 +371,14 @@ fn next_schedule_always_points_to_next_work_plan_item() {
 		assert_ok!(CoretimeAssigner::assign_core(
 			core_idx,
 			BlockNumberFor::<Test>::from(start_5),
-			default_test_assignments(),
+			vec![(CoreAssignment::Pool, PartsOf57600(28800))],
+			None,
+		));
+		// Test updating last entry once more:
+		assert_ok!(CoretimeAssigner::assign_core(
+			core_idx,
+			BlockNumberFor::<Test>::from(start_5),
+			vec![(CoreAssignment::Idle, PartsOf57600(28800))],
 			None,
 		));
 

prdoc/pr_6384.prdoc

@@ -0,0 +1,12 @@
+title: Relax requirements on `assign_core`.
+doc:
+- audience: Runtime Dev
+  description: |-
+    Relax requirements for `assign_core` so that it accepts updates for the last scheduled entry.
+    This will allow the coretime chain to split up assignments into multiple
+    messages, which allows for interlacing down to single block granularity.
+
+    Fixes: https://github.com/paritytech/polkadot-sdk/issues/6102
+crates:
+- name: polkadot-runtime-parachains
+  bump: major