Enable async backing on asset-hub-rococo (#2826)

The goal is to move all system chains on Rococo (+ other testnets?) to
use async backing.

Starting with `asset-hub-rococo` to get feedback, before I do the rest.

## Related

Example: https://github.com/paritytech/polkadot-sdk/pull/1619/
Guide:
https://github.com/w3f/polkadot-wiki/blob/master/docs/maintain/maintain-guides-async-backing.md

---------

Co-authored-by: Branislav Kontur <bkontur@gmail.com>
Co-authored-by: Dónal Murray <donal.murray@parity.io>

Cargo.lock

@@ -864,6 +864,7 @@ dependencies = [
  "cumulus-pallet-session-benchmarking",
  "cumulus-pallet-xcm",
  "cumulus-pallet-xcmp-queue",
+ "cumulus-primitives-aura",
  "cumulus-primitives-core",
  "cumulus-primitives-utility",
  "frame-benchmarking",

cumulus/client/collator/src/lib.rs

@@ -242,17 +242,19 @@ pub async fn initialize_collator_subsystems(
 	overseer_handle: &mut OverseerHandle,
 	key: CollatorPair,
 	para_id: ParaId,
+	reinitialize: bool,
 ) {
-	overseer_handle
+	let config = CollationGenerationConfig { key, para_id, collator: None };
-		.send_msg(
+
-			CollationGenerationMessage::Initialize(CollationGenerationConfig {
+	if reinitialize {
-				key,
+		overseer_handle
-				para_id,
+			.send_msg(CollationGenerationMessage::Reinitialize(config), "StartCollator")
-				collator: None,
+			.await;
-			}),
+	} else {
-			"StartCollator",
+		overseer_handle
-		)
+			.send_msg(CollationGenerationMessage::Initialize(config), "StartCollator")
-		.await;
+			.await;
+	}
 
 	overseer_handle
 		.send_msg(CollatorProtocolMessage::CollateOn(para_id), "StartCollator")

cumulus/client/consensus/aura/src/collators/lookahead.rs

@@ -105,6 +105,8 @@ pub struct Params<BI, CIDP, Client, Backend, RClient, CHP, SO, Proposer, CS> {
 	pub collator_service: CS,
 	/// The amount of time to spend authoring each block.
 	pub authoring_duration: Duration,
+	/// Whether we should reinitialize the collator config (i.e. we are transitioning to aura).
+	pub reinitialize: bool,
 }
 
 /// Run async-backing-friendly Aura.
@@ -149,6 +151,7 @@ where
 			&mut params.overseer_handle,
 			params.collator_key,
 			params.para_id,
+			params.reinitialize,
 		)
 		.await;
 

cumulus/parachains/runtimes/assets/asset-hub-rococo/Cargo.toml

@@ -77,6 +77,7 @@ cumulus-pallet-parachain-system = { path = "../../../../pallets/parachain-system
 cumulus-pallet-session-benchmarking = { path = "../../../../pallets/session-benchmarking", default-features = false }
 cumulus-pallet-xcm = { path = "../../../../pallets/xcm", default-features = false }
 cumulus-pallet-xcmp-queue = { path = "../../../../pallets/xcmp-queue", default-features = false, features = ["bridging"] }
+cumulus-primitives-aura = { path = "../../../../primitives/aura", default-features = false }
 cumulus-primitives-core = { path = "../../../../primitives/core", default-features = false }
 cumulus-primitives-utility = { path = "../../../../primitives/utility", default-features = false }
 pallet-collator-selection = { path = "../../../../pallets/collator-selection", default-features = false }
@@ -188,6 +189,7 @@ std = [
 	"cumulus-pallet-session-benchmarking/std",
 	"cumulus-pallet-xcm/std",
 	"cumulus-pallet-xcmp-queue/std",
+	"cumulus-primitives-aura/std",
 	"cumulus-primitives-core/std",
 	"cumulus-primitives-utility/std",
 	"frame-benchmarking?/std",

cumulus/parachains/runtimes/assets/asset-hub-rococo/src/lib.rs

@@ -33,7 +33,7 @@ use assets_common::{
 	matching::{FromNetwork, FromSiblingParachain},
 	AssetIdForTrustBackedAssetsConvert,
 };
-use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
+use cumulus_pallet_parachain_system::RelayNumberMonotonicallyIncreases;
 use cumulus_primitives_core::AggregateMessageOrigin;
 use parachains_common::rococo::snowbridge::EthereumNetwork;
 use sp_api::impl_runtime_apis;
@@ -62,7 +62,7 @@ use frame_support::{
 		ConstU128, ConstU32, ConstU64, ConstU8, EitherOfDiverse, Equals, InstanceFilter,
 		TransformOrigin,
 	},
-	weights::{ConstantMultiplier, Weight},
+	weights::{constants::WEIGHT_REF_TIME_PER_SECOND, ConstantMultiplier, Weight},
 	BoundedVec, PalletId,
 };
 use frame_system::{
@@ -71,14 +71,13 @@ use frame_system::{
 };
 use pallet_asset_conversion_tx_payment::AssetConversionAdapter;
 use pallet_nfts::PalletFeatures;
-pub use parachains_common as common;
 use parachains_common::{
 	impls::DealWithFees,
 	message_queue::{NarrowOriginToSibling, ParaIdToSibling},
 	rococo::{consensus::*, currency::*, fee::WeightToFee},
 	AccountId, AssetIdForTrustBackedAssets, AuraId, Balance, BlockNumber, CollectionId, Hash,
 	Header, ItemId, Nonce, Signature, AVERAGE_ON_INITIALIZE_RATIO, DAYS, HOURS,
-	MAXIMUM_BLOCK_WEIGHT, NORMAL_DISPATCH_RATIO, SLOT_DURATION,
+	NORMAL_DISPATCH_RATIO,
 };
 use sp_runtime::{Perbill, RuntimeDebug};
 use xcm_config::{
@@ -141,6 +140,28 @@ pub fn native_version() -> NativeVersion {
 	NativeVersion { runtime_version: VERSION, can_author_with: Default::default() }
 }
 
+/// We allow for 2 seconds of compute with a 6 second average block.
+const MAXIMUM_BLOCK_WEIGHT: Weight = Weight::from_parts(
+	WEIGHT_REF_TIME_PER_SECOND.saturating_mul(2),
+	cumulus_primitives_core::relay_chain::MAX_POV_SIZE as u64,
+);
+
+/// Maximum number of blocks simultaneously accepted by the Runtime, not yet included
+/// into the relay chain.
+const UNINCLUDED_SEGMENT_CAPACITY: u32 = 3;
+/// How many parachain blocks are processed by the relay chain per parent. Limits the
+/// number of blocks authored per slot.
+const BLOCK_PROCESSING_VELOCITY: u32 = 1;
+
+/// This determines the average expected block time that we are targeting.
+/// Blocks will be produced at a minimum duration defined by `SLOT_DURATION`.
+/// `SLOT_DURATION` is picked up by `pallet_timestamp` which is in turn picked
+/// up by `pallet_aura` to implement `fn slot_duration()`.
+///
+/// Change this to adjust the block time.
+pub const MILLISECS_PER_BLOCK: u64 = 6000;
+pub const SLOT_DURATION: u64 = MILLISECS_PER_BLOCK;
+
 parameter_types! {
 	pub const Version: RuntimeVersion = VERSION;
 	pub RuntimeBlockLength: BlockLength =
@@ -189,6 +210,9 @@ impl pallet_timestamp::Config for Runtime {
 	/// A timestamp: milliseconds since the unix epoch.
 	type Moment = u64;
 	type OnTimestampSet = Aura;
+	#[cfg(feature = "experimental")]
+	type MinimumPeriod = ConstU64<0>;
+	#[cfg(not(feature = "experimental"))]
 	type MinimumPeriod = ConstU64<{ SLOT_DURATION / 2 }>;
 	type WeightInfo = weights::pallet_timestamp::WeightInfo<Runtime>;
 }
@@ -630,15 +654,17 @@ impl cumulus_pallet_parachain_system::Config for Runtime {
 	type OutboundXcmpMessageSource = XcmpQueue;
 	type XcmpMessageHandler = XcmpQueue;
 	type ReservedXcmpWeight = ReservedXcmpWeight;
-	type CheckAssociatedRelayNumber = RelayNumberStrictlyIncreases;
+	type CheckAssociatedRelayNumber = RelayNumberMonotonicallyIncreases;
-	type ConsensusHook = cumulus_pallet_aura_ext::FixedVelocityConsensusHook<
+	type ConsensusHook = ConsensusHook;
-		Runtime,
-		RELAY_CHAIN_SLOT_DURATION_MILLIS,
-		BLOCK_PROCESSING_VELOCITY,
-		UNINCLUDED_SEGMENT_CAPACITY,
-	>;
 }
 
+type ConsensusHook = cumulus_pallet_aura_ext::FixedVelocityConsensusHook<
+	Runtime,
+	RELAY_CHAIN_SLOT_DURATION_MILLIS,
+	BLOCK_PROCESSING_VELOCITY,
+	UNINCLUDED_SEGMENT_CAPACITY,
+>;
+
 parameter_types! {
 	pub MessageQueueServiceWeight: Weight = Perbill::from_percent(35) * RuntimeBlockWeights::get().max_block;
 }
@@ -722,9 +748,9 @@ impl pallet_aura::Config for Runtime {
 	type AuthorityId = AuraId;
 	type DisabledValidators = ();
 	type MaxAuthorities = ConstU32<100_000>;
-	type AllowMultipleBlocksPerSlot = ConstBool<false>;
+	type AllowMultipleBlocksPerSlot = ConstBool<true>;
 	#[cfg(feature = "experimental")]
-	type SlotDuration = pallet_aura::MinimumPeriodTimesTwo<Self>;
+	type SlotDuration = ConstU64<SLOT_DURATION>;
 }
 
 parameter_types! {
@@ -1067,7 +1093,7 @@ mod benches {
 impl_runtime_apis! {
 	impl sp_consensus_aura::AuraApi<Block, AuraId> for Runtime {
 		fn slot_duration() -> sp_consensus_aura::SlotDuration {
-			sp_consensus_aura::SlotDuration::from_millis(Aura::slot_duration())
+			sp_consensus_aura::SlotDuration::from_millis(SLOT_DURATION)
 		}
 
 		fn authorities() -> Vec<AuraId> {
@@ -1075,6 +1101,15 @@ impl_runtime_apis! {
 		}
 	}
 
+	impl cumulus_primitives_aura::AuraUnincludedSegmentApi<Block> for Runtime {
+		fn can_build_upon(
+			included_hash: <Block as BlockT>::Hash,
+			slot: cumulus_primitives_aura::Slot,
+		) -> bool {
+			ConsensusHook::can_build_upon(included_hash, slot)
+		}
+	}
+
 	impl sp_api::Core<Block> for Runtime {
 		fn version() -> RuntimeVersion {
 			VERSION

cumulus/parachains/runtimes/assets/asset-hub-rococo/tests/tests.rs

@@ -28,10 +28,11 @@ use asset_hub_rococo_runtime::{
 	AllPalletsWithoutSystem, AssetConversion, AssetDeposit, Assets, Balances, CollatorSelection,
 	ExistentialDeposit, ForeignAssets, ForeignAssetsInstance, MetadataDepositBase,
 	MetadataDepositPerByte, ParachainSystem, Runtime, RuntimeCall, RuntimeEvent, SessionKeys,
-	ToWestendXcmRouterInstance, TrustBackedAssetsInstance, XcmpQueue,
+	ToWestendXcmRouterInstance, TrustBackedAssetsInstance, XcmpQueue, SLOT_DURATION,
 };
 use asset_test_utils::{
-	test_cases_over_bridge::TestBridgingConfig, CollatorSessionKey, CollatorSessionKeys, ExtBuilder,
+	test_cases_over_bridge::TestBridgingConfig, CollatorSessionKey, CollatorSessionKeys,
+	ExtBuilder, SlotDurations,
 };
 use codec::{Decode, Encode};
 use cumulus_primitives_utility::ChargeWeightInFungibles;
@@ -46,9 +47,10 @@ use frame_support::{
 	weights::{Weight, WeightToFee as WeightToFeeT},
 };
 use parachains_common::{
-	rococo::{currency::UNITS, fee::WeightToFee},
+	rococo::{consensus::RELAY_CHAIN_SLOT_DURATION_MILLIS, currency::UNITS, fee::WeightToFee},
 	AccountId, AssetIdForTrustBackedAssets, AuraId, Balance,
 };
+use sp_consensus_aura::SlotDuration;
 use sp_runtime::traits::MaybeEquivalence;
 use std::convert::Into;
 use xcm::latest::prelude::{Assets as XcmAssets, *};
@@ -78,6 +80,13 @@ fn collator_session_keys() -> CollatorSessionKeys<Runtime> {
 	CollatorSessionKeys::default().add(collator_session_key(ALICE))
 }
 
+fn slot_durations() -> SlotDurations {
+	SlotDurations {
+		relay: SlotDuration::from_millis(RELAY_CHAIN_SLOT_DURATION_MILLIS.into()),
+		para: SlotDuration::from_millis(SLOT_DURATION),
+	}
+}
+
 #[test]
 fn test_buy_and_refund_weight_in_native() {
 	ExtBuilder::<Runtime>::default()
@@ -892,6 +901,7 @@ asset_test_utils::include_teleports_for_native_asset_works!(
 	WeightToFee,
 	ParachainSystem,
 	collator_session_keys(),
+	slot_durations(),
 	ExistentialDeposit::get(),
 	Box::new(|runtime_event_encoded: Vec<u8>| {
 		match RuntimeEvent::decode(&mut &runtime_event_encoded[..]) {
@@ -912,6 +922,7 @@ asset_test_utils::include_teleports_for_foreign_assets_works!(
 	ForeignCreatorsSovereignAccountOf,
 	ForeignAssetsInstance,
 	collator_session_keys(),
+	slot_durations(),
 	ExistentialDeposit::get(),
 	Box::new(|runtime_event_encoded: Vec<u8>| {
 		match RuntimeEvent::decode(&mut &runtime_event_encoded[..]) {
@@ -1023,6 +1034,7 @@ fn limited_reserve_transfer_assets_for_native_asset_over_bridge_works(
 		LocationToAccountId,
 	>(
 		collator_session_keys(),
+		slot_durations(),
 		ExistentialDeposit::get(),
 		AccountId::from(ALICE),
 		Box::new(|runtime_event_encoded: Vec<u8>| {
@@ -1194,6 +1206,7 @@ mod asset_hub_rococo_tests {
 			LocationToAccountId,
 		>(
 			collator_session_keys(),
+			slot_durations(),
 			ExistentialDeposit::get(),
 			AccountId::from(ALICE),
 			Box::new(|runtime_event_encoded: Vec<u8>| {

cumulus/parachains/runtimes/assets/asset-hub-westend/src/lib.rs

@@ -55,7 +55,6 @@ use frame_system::{
 use pallet_asset_conversion_tx_payment::AssetConversionAdapter;
 use pallet_nfts::{DestroyWitness, PalletFeatures};
 use pallet_xcm::EnsureXcm;
-pub use parachains_common as common;
 use parachains_common::{
 	impls::DealWithFees,
 	message_queue::*,

cumulus/parachains/runtimes/assets/asset-hub-westend/tests/tests.rs

@@ -32,7 +32,8 @@ use asset_hub_westend_runtime::{
 };
 pub use asset_hub_westend_runtime::{AssetConversion, AssetDeposit, CollatorSelection, System};
 use asset_test_utils::{
-	test_cases_over_bridge::TestBridgingConfig, CollatorSessionKey, CollatorSessionKeys, ExtBuilder,
+	test_cases_over_bridge::TestBridgingConfig, CollatorSessionKey, CollatorSessionKeys,
+	ExtBuilder, SlotDurations,
 };
 use codec::{Decode, Encode};
 use cumulus_primitives_utility::ChargeWeightInFungibles;
@@ -47,9 +48,10 @@ use frame_support::{
 	weights::{Weight, WeightToFee as WeightToFeeT},
 };
 use parachains_common::{
-	westend::{currency::UNITS, fee::WeightToFee},
+	westend::{consensus::RELAY_CHAIN_SLOT_DURATION_MILLIS, currency::UNITS, fee::WeightToFee},
-	AccountId, AssetIdForTrustBackedAssets, AuraId, Balance,
+	AccountId, AssetIdForTrustBackedAssets, AuraId, Balance, SLOT_DURATION,
 };
+use sp_consensus_aura::SlotDuration;
 use sp_runtime::traits::MaybeEquivalence;
 use std::convert::Into;
 use xcm::latest::prelude::{Assets as XcmAssets, *};
@@ -79,6 +81,13 @@ fn collator_session_keys() -> CollatorSessionKeys<Runtime> {
 	CollatorSessionKeys::default().add(collator_session_key(ALICE))
 }
 
+fn slot_durations() -> SlotDurations {
+	SlotDurations {
+		relay: SlotDuration::from_millis(RELAY_CHAIN_SLOT_DURATION_MILLIS.into()),
+		para: SlotDuration::from_millis(SLOT_DURATION),
+	}
+}
+
 #[test]
 fn test_buy_and_refund_weight_in_native() {
 	ExtBuilder::<Runtime>::default()
@@ -895,6 +904,7 @@ asset_test_utils::include_teleports_for_native_asset_works!(
 	WeightToFee,
 	ParachainSystem,
 	collator_session_keys(),
+	slot_durations(),
 	ExistentialDeposit::get(),
 	Box::new(|runtime_event_encoded: Vec<u8>| {
 		match RuntimeEvent::decode(&mut &runtime_event_encoded[..]) {
@@ -915,6 +925,7 @@ asset_test_utils::include_teleports_for_foreign_assets_works!(
 	ForeignCreatorsSovereignAccountOf,
 	ForeignAssetsInstance,
 	collator_session_keys(),
+	slot_durations(),
 	ExistentialDeposit::get(),
 	Box::new(|runtime_event_encoded: Vec<u8>| {
 		match RuntimeEvent::decode(&mut &runtime_event_encoded[..]) {
@@ -1041,6 +1052,7 @@ fn limited_reserve_transfer_assets_for_native_asset_to_asset_hub_rococo_works()
 		LocationToAccountId,
 	>(
 		collator_session_keys(),
+		slot_durations(),
 		ExistentialDeposit::get(),
 		AccountId::from(ALICE),
 		Box::new(|runtime_event_encoded: Vec<u8>| {
@@ -1208,6 +1220,7 @@ fn reserve_transfer_native_asset_to_non_teleport_para_works() {
 		LocationToAccountId,
 	>(
 		collator_session_keys(),
+		slot_durations(),
 		ExistentialDeposit::get(),
 		AccountId::from(ALICE),
 		Box::new(|runtime_event_encoded: Vec<u8>| {

cumulus/parachains/runtimes/assets/test-utils/src/test_cases.rs

@@ -31,7 +31,7 @@ use frame_system::pallet_prelude::BlockNumberFor;
 use parachains_common::{AccountId, Balance};
 use parachains_runtimes_test_utils::{
 	assert_metadata, assert_total, mock_open_hrmp_channel, AccountIdOf, BalanceOf,
-	CollatorSessionKeys, ExtBuilder, ValidatorIdOf, XcmReceivedFrom,
+	CollatorSessionKeys, ExtBuilder, SlotDurations, ValidatorIdOf, XcmReceivedFrom,
 };
 use sp_runtime::{
 	traits::{MaybeEquivalence, StaticLookup, Zero},
@@ -57,6 +57,7 @@ pub fn teleports_for_native_asset_works<
 	HrmpChannelOpener,
 >(
 	collator_session_keys: CollatorSessionKeys<Runtime>,
+	slot_durations: SlotDurations,
 	existential_deposit: BalanceOf<Runtime>,
 	target_account: AccountIdOf<Runtime>,
 	unwrap_pallet_xcm_event: Box<dyn Fn(Vec<u8>) -> Option<pallet_xcm::Event<Runtime>>>,
@@ -205,6 +206,7 @@ pub fn teleports_for_native_asset_works<
 					None,
 					included_head.clone(),
 					&alice,
+					&slot_durations,
 				));
 
 				// check balances
@@ -257,6 +259,7 @@ pub fn teleports_for_native_asset_works<
 						Some((runtime_para_id, other_para_id)),
 						included_head,
 						&alice,
+						&slot_durations,
 					),
 					Err(DispatchError::Module(sp_runtime::ModuleError {
 						index: 31,
@@ -288,6 +291,7 @@ macro_rules! include_teleports_for_native_asset_works(
 		$weight_to_fee:path,
 		$hrmp_channel_opener:path,
 		$collator_session_key:expr,
+		$slot_durations:expr,
 		$existential_deposit:expr,
 		$unwrap_pallet_xcm_event:expr,
 		$runtime_para_id:expr
@@ -306,6 +310,7 @@ macro_rules! include_teleports_for_native_asset_works(
 				$hrmp_channel_opener
 			>(
 				$collator_session_key,
+				$slot_durations,
 				$existential_deposit,
 				target_account,
 				$unwrap_pallet_xcm_event,
@@ -328,6 +333,7 @@ pub fn teleports_for_foreign_assets_works<
 	ForeignAssetsPalletInstance,
 >(
 	collator_session_keys: CollatorSessionKeys<Runtime>,
+	slot_durations: SlotDurations,
 	target_account: AccountIdOf<Runtime>,
 	existential_deposit: BalanceOf<Runtime>,
 	asset_owner: AccountIdOf<Runtime>,
@@ -592,6 +598,7 @@ pub fn teleports_for_foreign_assets_works<
 					Some((runtime_para_id, foreign_para_id)),
 					included_head,
 					&alice,
+					&slot_durations,
 				));
 
 				// check balances
@@ -644,6 +651,7 @@ macro_rules! include_teleports_for_foreign_assets_works(
 		$sovereign_account_of:path,
 		$assets_pallet_instance:path,
 		$collator_session_key:expr,
+		$slot_durations:expr,
 		$existential_deposit:expr,
 		$unwrap_pallet_xcm_event:expr,
 		$unwrap_xcmp_queue_event:expr
@@ -666,6 +674,7 @@ macro_rules! include_teleports_for_foreign_assets_works(
 				$assets_pallet_instance
 			>(
 				$collator_session_key,
+				$slot_durations,
 				target_account,
 				$existential_deposit,
 				asset_owner,
@@ -1397,6 +1406,7 @@ pub fn reserve_transfer_native_asset_to_non_teleport_para_works<
 	LocationToAccountId,
 >(
 	collator_session_keys: CollatorSessionKeys<Runtime>,
+	slot_durations: SlotDurations,
 	existential_deposit: BalanceOf<Runtime>,
 	alice_account: AccountIdOf<Runtime>,
 	unwrap_pallet_xcm_event: Box<dyn Fn(Vec<u8>) -> Option<pallet_xcm::Event<Runtime>>>,
@@ -1470,6 +1480,7 @@ pub fn reserve_transfer_native_asset_to_non_teleport_para_works<
 				other_para_id.into(),
 				included_head,
 				&alice,
+				&slot_durations,
 			);
 
 			// we calculate exact delivery fees _after_ sending the message by weighing the sent

cumulus/parachains/runtimes/assets/test-utils/src/test_cases_over_bridge.rs

@@ -27,7 +27,7 @@ use frame_system::pallet_prelude::BlockNumberFor;
 use parachains_common::{AccountId, Balance};
 use parachains_runtimes_test_utils::{
 	mock_open_hrmp_channel, AccountIdOf, BalanceOf, CollatorSessionKeys, ExtBuilder, RuntimeHelper,
-	ValidatorIdOf, XcmReceivedFrom,
+	SlotDurations, ValidatorIdOf, XcmReceivedFrom,
 };
 use sp_runtime::{traits::StaticLookup, Saturating};
 use sp_std::ops::Mul;
@@ -52,6 +52,7 @@ pub fn limited_reserve_transfer_assets_for_native_asset_works<
 	LocationToAccountId,
 >(
 	collator_session_keys: CollatorSessionKeys<Runtime>,
+	slot_durations: SlotDurations,
 	existential_deposit: BalanceOf<Runtime>,
 	alice_account: AccountIdOf<Runtime>,
 	unwrap_pallet_xcm_event: Box<dyn Fn(Vec<u8>) -> Option<pallet_xcm::Event<Runtime>>>,
@@ -125,6 +126,7 @@ pub fn limited_reserve_transfer_assets_for_native_asset_works<
 				local_bridge_hub_para_id.into(),
 				included_head,
 				&alice,
+				&slot_durations,
 			);
 
 			// we calculate exact delivery fees _after_ sending the message by weighing the sent

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-rococo/tests/tests.rs

@@ -24,9 +24,14 @@ use bridge_hub_rococo_runtime::{
 	Executive, ExistentialDeposit, ParachainSystem, PolkadotXcm, Runtime, RuntimeCall,
 	RuntimeEvent, RuntimeOrigin, SessionKeys, SignedExtra, TransactionPayment, UncheckedExtrinsic,
 };
+use bridge_hub_test_utils::SlotDurations;
 use codec::{Decode, Encode};
 use frame_support::{dispatch::GetDispatchInfo, parameter_types, traits::ConstU8};
-use parachains_common::{rococo::fee::WeightToFee, AccountId, AuraId, Balance};
+use parachains_common::{
+	rococo::{consensus::RELAY_CHAIN_SLOT_DURATION_MILLIS, fee::WeightToFee},
+	AccountId, AuraId, Balance, SLOT_DURATION,
+};
+use sp_consensus_aura::SlotDuration;
 use sp_core::H160;
 use sp_keyring::AccountKeyring::Alice;
 use sp_runtime::{
@@ -95,6 +100,13 @@ fn collator_session_keys() -> bridge_hub_test_utils::CollatorSessionKeys<Runtime
 	)
 }
 
+fn slot_durations() -> SlotDurations {
+	SlotDurations {
+		relay: SlotDuration::from_millis(RELAY_CHAIN_SLOT_DURATION_MILLIS.into()),
+		para: SlotDuration::from_millis(SLOT_DURATION),
+	}
+}
+
 bridge_hub_test_utils::test_cases::include_teleports_for_native_asset_works!(
 	Runtime,
 	AllPalletsWithoutSystem,
@@ -103,6 +115,7 @@ bridge_hub_test_utils::test_cases::include_teleports_for_native_asset_works!(
 	WeightToFee,
 	ParachainSystem,
 	collator_session_keys(),
+	slot_durations(),
 	ExistentialDeposit::get(),
 	Box::new(|runtime_event_encoded: Vec<u8>| {
 		match RuntimeEvent::decode(&mut &runtime_event_encoded[..]) {
@@ -264,6 +277,7 @@ mod bridge_hub_westend_tests {
 			ConstU8<2>,
 		>(
 			collator_session_keys(),
+			slot_durations(),
 			bp_bridge_hub_rococo::BRIDGE_HUB_ROCOCO_PARACHAIN_ID,
 			SIBLING_PARACHAIN_ID,
 			Box::new(|runtime_event_encoded: Vec<u8>| {
@@ -288,6 +302,7 @@ mod bridge_hub_westend_tests {
 		// from Westend
 		from_parachain::relayed_incoming_message_works::<RuntimeTestsAdapter>(
 			collator_session_keys(),
+			slot_durations(),
 			bp_bridge_hub_rococo::BRIDGE_HUB_ROCOCO_PARACHAIN_ID,
 			bp_bridge_hub_westend::BRIDGE_HUB_WESTEND_PARACHAIN_ID,
 			BridgeHubWestendChainId::get(),
@@ -304,6 +319,7 @@ mod bridge_hub_westend_tests {
 		// for Westend
 		from_parachain::complex_relay_extrinsic_works::<RuntimeTestsAdapter>(
 			collator_session_keys(),
+			slot_durations(),
 			bp_bridge_hub_rococo::BRIDGE_HUB_ROCOCO_PARACHAIN_ID,
 			bp_bridge_hub_westend::BRIDGE_HUB_WESTEND_PARACHAIN_ID,
 			SIBLING_PARACHAIN_ID,
@@ -459,6 +475,7 @@ mod bridge_hub_bulletin_tests {
 			ConstU8<2>,
 		>(
 			collator_session_keys(),
+			slot_durations(),
 			bp_bridge_hub_rococo::BRIDGE_HUB_ROCOCO_PARACHAIN_ID,
 			SIBLING_PARACHAIN_ID,
 			Box::new(|runtime_event_encoded: Vec<u8>| {
@@ -483,6 +500,7 @@ mod bridge_hub_bulletin_tests {
 		// from Bulletin
 		from_grandpa_chain::relayed_incoming_message_works::<RuntimeTestsAdapter>(
 			collator_session_keys(),
+			slot_durations(),
 			bp_bridge_hub_rococo::BRIDGE_HUB_ROCOCO_PARACHAIN_ID,
 			RococoBulletinChainId::get(),
 			SIBLING_PARACHAIN_ID,
@@ -498,6 +516,7 @@ mod bridge_hub_bulletin_tests {
 		// for Bulletin
 		from_grandpa_chain::complex_relay_extrinsic_works::<RuntimeTestsAdapter>(
 			collator_session_keys(),
+			slot_durations(),
 			bp_bridge_hub_rococo::BRIDGE_HUB_ROCOCO_PARACHAIN_ID,
 			SIBLING_PARACHAIN_ID,
 			RococoBulletinChainId::get(),

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-westend/tests/tests.rs

@@ -18,7 +18,7 @@
 
 use bp_polkadot_core::Signature;
 use bridge_common_config::{DeliveryRewardInBalance, RequiredStakeForStakeAndSlash};
-use bridge_hub_test_utils::test_cases::from_parachain;
+use bridge_hub_test_utils::{test_cases::from_parachain, SlotDurations};
 use bridge_hub_westend_runtime::{
 	bridge_common_config, bridge_to_rococo_config,
 	xcm_config::{RelayNetwork, WestendLocation, XcmConfig},
@@ -33,7 +33,11 @@ use bridge_to_rococo_config::{
 };
 use codec::{Decode, Encode};
 use frame_support::{dispatch::GetDispatchInfo, parameter_types, traits::ConstU8};
-use parachains_common::{westend::fee::WeightToFee, AccountId, AuraId, Balance};
+use parachains_common::{
+	westend::{consensus::RELAY_CHAIN_SLOT_DURATION_MILLIS, fee::WeightToFee},
+	AccountId, AuraId, Balance, SLOT_DURATION,
+};
+use sp_consensus_aura::SlotDuration;
 use sp_keyring::AccountKeyring::Alice;
 use sp_runtime::{
 	generic::{Era, SignedPayload},
@@ -111,6 +115,13 @@ fn collator_session_keys() -> bridge_hub_test_utils::CollatorSessionKeys<Runtime
 	)
 }
 
+fn slot_durations() -> SlotDurations {
+	SlotDurations {
+		relay: SlotDuration::from_millis(RELAY_CHAIN_SLOT_DURATION_MILLIS.into()),
+		para: SlotDuration::from_millis(SLOT_DURATION),
+	}
+}
+
 bridge_hub_test_utils::test_cases::include_teleports_for_native_asset_works!(
 	Runtime,
 	AllPalletsWithoutSystem,
@@ -119,6 +130,7 @@ bridge_hub_test_utils::test_cases::include_teleports_for_native_asset_works!(
 	WeightToFee,
 	ParachainSystem,
 	collator_session_keys(),
+	slot_durations(),
 	ExistentialDeposit::get(),
 	Box::new(|runtime_event_encoded: Vec<u8>| {
 		match RuntimeEvent::decode(&mut &runtime_event_encoded[..]) {
@@ -229,6 +241,7 @@ fn message_dispatch_routing_works() {
 		ConstU8<2>,
 	>(
 		collator_session_keys(),
+		slot_durations(),
 		bp_bridge_hub_westend::BRIDGE_HUB_WESTEND_PARACHAIN_ID,
 		SIBLING_PARACHAIN_ID,
 		Box::new(|runtime_event_encoded: Vec<u8>| {
@@ -252,6 +265,7 @@ fn message_dispatch_routing_works() {
 fn relayed_incoming_message_works() {
 	from_parachain::relayed_incoming_message_works::<RuntimeTestsAdapter>(
 		collator_session_keys(),
+		slot_durations(),
 		bp_bridge_hub_westend::BRIDGE_HUB_WESTEND_PARACHAIN_ID,
 		bp_bridge_hub_rococo::BRIDGE_HUB_ROCOCO_PARACHAIN_ID,
 		BridgeHubRococoChainId::get(),
@@ -267,6 +281,7 @@ fn relayed_incoming_message_works() {
 pub fn complex_relay_extrinsic_works() {
 	from_parachain::complex_relay_extrinsic_works::<RuntimeTestsAdapter>(
 		collator_session_keys(),
+		slot_durations(),
 		bp_bridge_hub_westend::BRIDGE_HUB_WESTEND_PARACHAIN_ID,
 		bp_bridge_hub_rococo::BRIDGE_HUB_ROCOCO_PARACHAIN_ID,
 		SIBLING_PARACHAIN_ID,

cumulus/parachains/runtimes/bridge-hubs/test-utils/src/test_cases/from_grandpa_chain.rs

@@ -39,7 +39,7 @@ use bridge_runtime_common::{
 use frame_support::traits::{Get, OnFinalize, OnInitialize};
 use frame_system::pallet_prelude::BlockNumberFor;
 use parachains_runtimes_test_utils::{
-	AccountIdOf, BasicParachainRuntime, CollatorSessionKeys, RuntimeCallOf,
+	AccountIdOf, BasicParachainRuntime, CollatorSessionKeys, RuntimeCallOf, SlotDurations,
 };
 use sp_keyring::AccountKeyring::*;
 use sp_runtime::{traits::Header as HeaderT, AccountId32};
@@ -107,6 +107,7 @@ where
 /// Also verifies relayer transaction signed extensions work as intended.
 pub fn relayed_incoming_message_works<RuntimeHelper>(
 	collator_session_key: CollatorSessionKeys<RuntimeHelper::Runtime>,
+	slot_durations: SlotDurations,
 	runtime_para_id: u32,
 	bridged_chain_id: bp_runtime::ChainId,
 	sibling_parachain_id: u32,
@@ -136,6 +137,7 @@ pub fn relayed_incoming_message_works<RuntimeHelper>(
 		RuntimeHelper::MPI,
 	>(
 		collator_session_key,
+		slot_durations,
 		runtime_para_id,
 		sibling_parachain_id,
 		local_relay_chain_id,
@@ -205,6 +207,7 @@ pub fn relayed_incoming_message_works<RuntimeHelper>(
 /// Also verifies relayer transaction signed extensions work as intended.
 pub fn complex_relay_extrinsic_works<RuntimeHelper>(
 	collator_session_key: CollatorSessionKeys<RuntimeHelper::Runtime>,
+	slot_durations: SlotDurations,
 	runtime_para_id: u32,
 	sibling_parachain_id: u32,
 	bridged_chain_id: bp_runtime::ChainId,
@@ -237,6 +240,7 @@ pub fn complex_relay_extrinsic_works<RuntimeHelper>(
 		RuntimeHelper::MPI,
 	>(
 		collator_session_key,
+		slot_durations,
 		runtime_para_id,
 		sibling_parachain_id,
 		local_relay_chain_id,

cumulus/parachains/runtimes/bridge-hubs/test-utils/src/test_cases/from_parachain.rs

@@ -40,7 +40,7 @@ use bridge_runtime_common::{
 use frame_support::traits::{Get, OnFinalize, OnInitialize};
 use frame_system::pallet_prelude::BlockNumberFor;
 use parachains_runtimes_test_utils::{
-	AccountIdOf, BasicParachainRuntime, CollatorSessionKeys, RuntimeCallOf,
+	AccountIdOf, BasicParachainRuntime, CollatorSessionKeys, RuntimeCallOf, SlotDurations,
 };
 use sp_keyring::AccountKeyring::*;
 use sp_runtime::{traits::Header as HeaderT, AccountId32};
@@ -112,6 +112,7 @@ where
 /// Also verifies relayer transaction signed extensions work as intended.
 pub fn relayed_incoming_message_works<RuntimeHelper>(
 	collator_session_key: CollatorSessionKeys<RuntimeHelper::Runtime>,
+	slot_durations: SlotDurations,
 	runtime_para_id: u32,
 	bridged_para_id: u32,
 	bridged_chain_id: bp_runtime::ChainId,
@@ -146,6 +147,7 @@ pub fn relayed_incoming_message_works<RuntimeHelper>(
 		RuntimeHelper::MPI,
 	>(
 		collator_session_key,
+		slot_durations,
 		runtime_para_id,
 		sibling_parachain_id,
 		local_relay_chain_id,
@@ -244,6 +246,7 @@ pub fn relayed_incoming_message_works<RuntimeHelper>(
 /// Also verifies relayer transaction signed extensions work as intended.
 pub fn complex_relay_extrinsic_works<RuntimeHelper>(
 	collator_session_key: CollatorSessionKeys<RuntimeHelper::Runtime>,
+	slot_durations: SlotDurations,
 	runtime_para_id: u32,
 	bridged_para_id: u32,
 	sibling_parachain_id: u32,
@@ -281,6 +284,7 @@ pub fn complex_relay_extrinsic_works<RuntimeHelper>(
 		RuntimeHelper::MPI,
 	>(
 		collator_session_key,
+		slot_durations,
 		runtime_para_id,
 		sibling_parachain_id,
 		local_relay_chain_id,

cumulus/parachains/runtimes/bridge-hubs/test-utils/src/test_cases/helpers.rs

@@ -31,7 +31,7 @@ use frame_system::pallet_prelude::BlockNumberFor;
 use pallet_bridge_grandpa::{BridgedBlockHash, BridgedHeader};
 use parachains_common::AccountId;
 use parachains_runtimes_test_utils::{
-	mock_open_hrmp_channel, AccountIdOf, CollatorSessionKeys, RuntimeCallOf,
+	mock_open_hrmp_channel, AccountIdOf, CollatorSessionKeys, RuntimeCallOf, SlotDurations,
 };
 use sp_core::Get;
 use sp_keyring::AccountKeyring::*;
@@ -220,6 +220,7 @@ pub fn relayer_id_at_bridged_chain<Runtime: pallet_bridge_messages::Config<MPI>,
 /// with proofs (finality, message) independently submitted.
 pub fn relayed_incoming_message_works<Runtime, AllPalletsWithoutSystem, MPI>(
 	collator_session_key: CollatorSessionKeys<Runtime>,
+	slot_durations: SlotDurations,
 	runtime_para_id: u32,
 	sibling_parachain_id: u32,
 	local_relay_chain_id: NetworkId,
@@ -272,6 +273,7 @@ pub fn relayed_incoming_message_works<Runtime, AllPalletsWithoutSystem, MPI>(
 				sibling_parachain_id.into(),
 				included_head,
 				&alice,
+				&slot_durations,
 			);
 
 			// set up relayer details and proofs

cumulus/parachains/runtimes/bridge-hubs/test-utils/src/test_cases/mod.rs

@@ -45,7 +45,7 @@ use frame_system::pallet_prelude::BlockNumberFor;
 use parachains_common::AccountId;
 use parachains_runtimes_test_utils::{
 	mock_open_hrmp_channel, AccountIdOf, BalanceOf, CollatorSessionKeys, ExtBuilder, RuntimeCallOf,
-	XcmReceivedFrom,
+	SlotDurations, XcmReceivedFrom,
 };
 use sp_runtime::{traits::Zero, AccountId32};
 use xcm::{latest::prelude::*, AlwaysLatest};
@@ -419,6 +419,7 @@ pub fn message_dispatch_routing_works<
 	NetworkDistanceAsParentCount,
 >(
 	collator_session_key: CollatorSessionKeys<Runtime>,
+	slot_durations: SlotDurations,
 	runtime_para_id: u32,
 	sibling_parachain_id: u32,
 	unwrap_cumulus_pallet_parachain_system_event: Box<
@@ -529,6 +530,7 @@ pub fn message_dispatch_routing_works<
 			sibling_parachain_id.into(),
 			included_head,
 			&alice,
+			&slot_durations,
 		);
 		let result =
 			<<Runtime as BridgeMessagesConfig<MessagesPalletInstance>>::MessageDispatch>::dispatch(

cumulus/parachains/runtimes/test-utils/src/lib.rs

@@ -29,7 +29,6 @@ use frame_support::{
 	weights::Weight,
 };
 use frame_system::pallet_prelude::{BlockNumberFor, HeaderFor};
-use parachains_common::SLOT_DURATION;
 use polkadot_parachain_primitives::primitives::{
 	HeadData, HrmpChannelId, RelayChainBlockNumber, XcmpMessageFormat,
 };
@@ -115,6 +114,11 @@ impl<Runtime: frame_system::Config + pallet_balances::Config + pallet_session::C
 	}
 }
 
+pub struct SlotDurations {
+	pub relay: SlotDuration,
+	pub para: SlotDuration,
+}
+
 /// A set of traits for a minimal parachain runtime, that may be used in conjunction with the
 /// `ExtBuilder` and the `RuntimeHelper`.
 pub trait BasicParachainRuntime:
@@ -335,6 +339,7 @@ impl<
 		open_hrmp_channel: Option<(u32, u32)>,
 		included_head: HeaderFor<Runtime>,
 		slot_digest: &[u8],
+		slot_durations: &SlotDurations,
 	) -> DispatchResult
 	where
 		HrmpChannelOpener: frame_support::inherent::ProvideInherent<
@@ -348,6 +353,7 @@ impl<
 				target_para_id.into(),
 				included_head,
 				slot_digest,
+				slot_durations,
 			);
 		}
 
@@ -493,12 +499,12 @@ pub fn mock_open_hrmp_channel<
 	recipient: ParaId,
 	included_head: HeaderFor<C>,
 	mut slot_digest: &[u8],
+	slot_durations: &SlotDurations,
 ) {
-	const RELAY_CHAIN_SLOT_DURATION: SlotDuration = SlotDuration::from_millis(6000);
 	let slot = Slot::decode(&mut slot_digest).expect("failed to decode digest");
 	// Convert para slot to relay chain.
-	let timestamp = slot.saturating_mul(SLOT_DURATION);
+	let timestamp = slot.saturating_mul(slot_durations.para.as_millis());
-	let relay_slot = Slot::from_timestamp(timestamp.into(), RELAY_CHAIN_SLOT_DURATION);
+	let relay_slot = Slot::from_timestamp(timestamp.into(), slot_durations.relay);
 
 	let n = 1_u32;
 	let mut sproof_builder = RelayStateSproofBuilder {

cumulus/polkadot-parachain/src/command.rs

@@ -695,9 +695,7 @@ pub fn run() -> Result<()> {
 					.map(|r| r.0)
 					.map_err(Into::into),
 
-					AssetHubKusama |
+					AssetHubKusama | AssetHubWestend =>
-					AssetHubRococo |
-					AssetHubWestend =>
 						crate::service::start_asset_hub_node::<
 							RuntimeApi,
 							AuraId,
@@ -706,6 +704,15 @@ pub fn run() -> Result<()> {
 						.map(|r| r.0)
 						.map_err(Into::into),
 
+				    AssetHubRococo =>
+						crate::service::start_asset_hub_lookahead_node::<
+						RuntimeApi,
+							AuraId,
+						>(config, polkadot_config, collator_options, id, hwbench)
+						.await
+						.map(|r| r.0)
+						.map_err(Into::into),
+
 					CollectivesPolkadot | CollectivesWestend =>
 						crate::service::start_generic_aura_node::<
 							RuntimeApi,

cumulus/polkadot-parachain/src/service.rs

@@ -976,6 +976,7 @@ pub async fn start_rococo_parachain_node(
 				proposer,
 				collator_service,
 				authoring_duration: Duration::from_millis(1500),
+				reinitialize: false,
 			};
 
 			let fut = aura::run::<
@@ -1291,7 +1292,7 @@ where
 	Ok(BasicQueue::new(verifier, Box::new(block_import), None, &spawner, registry))
 }
 
-/// Start an aura powered parachain node. Asset Hub and Collectives use this.
+/// Start an aura powered parachain node. Collectives uses this.
 pub async fn start_generic_aura_node<RuntimeApi, AuraId: AppCrypto>(
 	parachain_config: Configuration,
 	polkadot_config: Configuration,
@@ -1530,6 +1531,159 @@ where
 	.await
 }
 
+/// Start a shell node which should later transition into an Aura powered parachain node. Asset Hub
+/// uses this because at genesis, Asset Hub was on the `shell` runtime which didn't have Aura and
+/// needs to sync and upgrade before it can run `AuraApi` functions.
+///
+/// Uses the lookahead collator to support async backing.
+#[sc_tracing::logging::prefix_logs_with("Parachain")]
+pub async fn start_asset_hub_lookahead_node<RuntimeApi, AuraId: AppCrypto + Send + Codec + Sync>(
+	parachain_config: Configuration,
+	polkadot_config: Configuration,
+	collator_options: CollatorOptions,
+	para_id: ParaId,
+	hwbench: Option<sc_sysinfo::HwBench>,
+) -> sc_service::error::Result<(TaskManager, Arc<ParachainClient<RuntimeApi>>)>
+where
+	RuntimeApi: ConstructRuntimeApi<Block, ParachainClient<RuntimeApi>> + Send + Sync + 'static,
+	RuntimeApi::RuntimeApi: sp_transaction_pool::runtime_api::TaggedTransactionQueue<Block>
+		+ sp_api::Metadata<Block>
+		+ sp_session::SessionKeys<Block>
+		+ sp_api::ApiExt<Block>
+		+ sp_offchain::OffchainWorkerApi<Block>
+		+ sp_block_builder::BlockBuilder<Block>
+		+ cumulus_primitives_core::CollectCollationInfo<Block>
+		+ sp_consensus_aura::AuraApi<Block, <<AuraId as AppCrypto>::Pair as Pair>::Public>
+		+ pallet_transaction_payment_rpc::TransactionPaymentRuntimeApi<Block, Balance>
+		+ frame_rpc_system::AccountNonceApi<Block, AccountId, Nonce>
+		+ cumulus_primitives_aura::AuraUnincludedSegmentApi<Block>,
+	<<AuraId as AppCrypto>::Pair as Pair>::Signature:
+		TryFrom<Vec<u8>> + std::hash::Hash + sp_runtime::traits::Member + Codec,
+{
+	start_node_impl::<RuntimeApi, _, _, _>(
+		parachain_config,
+		polkadot_config,
+		collator_options,
+		CollatorSybilResistance::Resistant, // Aura
+		para_id,
+		|_| Ok(RpcModule::new(())),
+		aura_build_import_queue::<_, AuraId>,
+		|client,
+		 block_import,
+		 prometheus_registry,
+		 telemetry,
+		 task_manager,
+		 relay_chain_interface,
+		 transaction_pool,
+		 sync_oracle,
+		 keystore,
+		 relay_chain_slot_duration,
+		 para_id,
+		 collator_key,
+		 overseer_handle,
+		 announce_block,
+		 backend| {
+			let relay_chain_interface2 = relay_chain_interface.clone();
+
+			let collator_service = CollatorService::new(
+				client.clone(),
+				Arc::new(task_manager.spawn_handle()),
+				announce_block,
+				client.clone(),
+			);
+
+			let spawner = task_manager.spawn_handle();
+
+			let proposer_factory = sc_basic_authorship::ProposerFactory::with_proof_recording(
+				spawner,
+				client.clone(),
+				transaction_pool,
+				prometheus_registry,
+				telemetry.clone(),
+			);
+
+			let collation_future = Box::pin(async move {
+				// Start collating with the `shell` runtime while waiting for an upgrade to an Aura
+				// compatible runtime.
+				let mut request_stream = cumulus_client_collator::relay_chain_driven::init(
+					collator_key.clone(),
+					para_id,
+					overseer_handle.clone(),
+				)
+				.await;
+				while let Some(request) = request_stream.next().await {
+					let pvd = request.persisted_validation_data().clone();
+					let last_head_hash =
+						match <Block as BlockT>::Header::decode(&mut &pvd.parent_head.0[..]) {
+							Ok(header) => header.hash(),
+							Err(e) => {
+								log::error!("Could not decode the head data: {e}");
+								request.complete(None);
+								continue
+							},
+						};
+
+					// Check if we have upgraded to an Aura compatible runtime and transition if
+					// necessary.
+					if client
+						.runtime_api()
+						.has_api::<dyn AuraApi<Block, AuraId>>(last_head_hash)
+						.unwrap_or(false)
+					{
+						// Respond to this request before transitioning to Aura.
+						request.complete(None);
+						break
+					}
+				}
+
+				// Move to Aura consensus.
+				let slot_duration = match cumulus_client_consensus_aura::slot_duration(&*client) {
+					Ok(d) => d,
+					Err(e) => {
+						log::error!("Could not get Aura slot duration: {e}");
+						return
+					},
+				};
+
+				let proposer = Proposer::new(proposer_factory);
+
+				let params = AuraParams {
+					create_inherent_data_providers: move |_, ()| async move { Ok(()) },
+					block_import,
+					para_client: client.clone(),
+					para_backend: backend,
+					relay_client: relay_chain_interface2,
+					code_hash_provider: move |block_hash| {
+						client.code_at(block_hash).ok().map(|c| ValidationCode::from(c).hash())
+					},
+					sync_oracle,
+					keystore,
+					collator_key,
+					para_id,
+					overseer_handle,
+					slot_duration,
+					relay_chain_slot_duration,
+					proposer,
+					collator_service,
+					authoring_duration: Duration::from_millis(1500),
+					reinitialize: true, /* we need to always re-initialize for asset-hub moving
+					                     * to aura */
+				};
+
+				aura::run::<Block, <AuraId as AppCrypto>::Pair, _, _, _, _, _, _, _, _, _>(params)
+					.await
+			});
+
+			let spawner = task_manager.spawn_essential_handle();
+			spawner.spawn_essential("cumulus-asset-hub-collator", None, collation_future);
+
+			Ok(())
+		},
+		hwbench,
+	)
+	.await
+}
+
 /// Start an aura powered parachain node which uses the lookahead collator to support async backing.
 /// This node is basic in the sense that its runtime api doesn't include common contents such as
 /// transaction payment. Used for aura glutton.
@@ -1615,6 +1769,7 @@ where
 				proposer,
 				collator_service,
 				authoring_duration: Duration::from_millis(1500),
+				reinitialize: false,
 			};
 
 			let fut =

polkadot/node/collation-generation/src/lib.rs

@@ -143,6 +143,16 @@ impl CollationGenerationSubsystem {
 				}
 				false
 			},
+			Ok(FromOrchestra::Communication {
+				msg: CollationGenerationMessage::Reinitialize(config),
+			}) => {
+				if self.config.is_none() {
+					gum::error!(target: LOG_TARGET, "no initial initialization");
+				} else {
+					self.config = Some(Arc::new(config));
+				}
+				false
+			},
 			Ok(FromOrchestra::Communication {
 				msg: CollationGenerationMessage::SubmitCollation(params),
 			}) => {

polkadot/node/subsystem-types/src/messages.rs

@@ -830,8 +830,10 @@ pub enum ProvisionerMessage {
 /// Message to the Collation Generation subsystem.
 #[derive(Debug)]
 pub enum CollationGenerationMessage {
-	/// Initialize the collation generation subsystem
+	/// Initialize the collation generation subsystem.
 	Initialize(CollationGenerationConfig),
+	/// Reinitialize the collation generation subsystem, overriding the existing config.
+	Reinitialize(CollationGenerationConfig),
 	/// Submit a collation to the subsystem. This will package it into a signed
 	/// [`CommittedCandidateReceipt`] and distribute along the network to validators.
 	///

prdoc/pr_2826.prdoc

@@ -0,0 +1,10 @@
+title: Enable async backing on asset-hub-rococo
+
+doc:
+  - audience: Runtime User
+    description: |
+      Async backing has been enabled on Asset Hub Rococo, which now targets 6s block times.
+
+crates:
+  - name: asset-hub-rococo-runtime
+  - name: polkadot-parachain-bin