Add UMP pricing (#1556)

# Description

Adds pricing for UMP, much like it was added for DMP in
paritytech/polkadot#6843 and HRMP in
#1234.

---------

Co-authored-by: command-bot <>
Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>

cumulus/pallets/parachain-system/Cargo.toml

@@ -29,6 +29,7 @@ sp-version = { path = "../../../substrate/primitives/version", default-features
 
 # Polkadot
 polkadot-parachain-primitives = { path = "../../../polkadot/parachain", default-features = false, features = [ "wasm-api" ]}
+polkadot-runtime-parachains = { path = "../../../polkadot/runtime/parachains", default-features = false }
 xcm = { package = "staging-xcm", path = "../../../polkadot/xcm", default-features = false}
 
 # Cumulus
@@ -63,6 +64,7 @@ std = [
 	"frame-system/std",
 	"log/std",
 	"polkadot-parachain-primitives/std",
+	"polkadot-runtime-parachains/std",
 	"scale-info/std",
 	"sp-core/std",
 	"sp-externalities/std",
@@ -80,12 +82,14 @@ runtime-benchmarks = [
 	"frame-support/runtime-benchmarks",
 	"frame-system/runtime-benchmarks",
 	"polkadot-parachain-primitives/runtime-benchmarks",
+	"polkadot-runtime-parachains/runtime-benchmarks",
 	"sp-runtime/runtime-benchmarks",
 ]
 
 try-runtime = [
 	"frame-support/try-runtime",
 	"frame-system/try-runtime",
+	"polkadot-runtime-parachains/try-runtime",
 	"sp-runtime/try-runtime",
 ]
 

cumulus/pallets/parachain-system/src/lib.rs

@@ -45,14 +45,15 @@ use frame_support::{
 };
 use frame_system::{ensure_none, ensure_root, pallet_prelude::HeaderFor};
 use polkadot_parachain_primitives::primitives::RelayChainBlockNumber;
+use polkadot_runtime_parachains::FeeTracker;
 use scale_info::TypeInfo;
 use sp_runtime::{
 	traits::{Block as BlockT, BlockNumberProvider, Hash},
 	transaction_validity::{
 		InvalidTransaction, TransactionLongevity, TransactionSource, TransactionValidity,
 		ValidTransaction,
 	},
-	DispatchError, RuntimeDebug,
+	DispatchError, FixedU128, RuntimeDebug, Saturating,
 };
 use sp_std::{cmp, collections::btree_map::BTreeMap, prelude::*};
 use xcm::latest::XcmHash;
@@ -177,6 +178,20 @@ where
 	check_version: bool,
 }
 
+pub mod ump_constants {
+	use super::FixedU128;
+
+	/// `host_config.max_upward_queue_size / THRESHOLD_FACTOR` is the threshold after which delivery
+	/// starts getting exponentially more expensive.
+	/// `2` means the price starts to increase when queue is half full.
+	pub const THRESHOLD_FACTOR: u32 = 2;
+	/// The base number the delivery fee factor gets multiplied by every time it is increased.
+	/// Also the number it gets divided by when decreased.
+	pub const EXPONENTIAL_FEE_BASE: FixedU128 = FixedU128::from_rational(105, 100); // 1.05
+	/// The base number message size in KB is multiplied by before increasing the fee factor.
+	pub const MESSAGE_SIZE_FEE_BASE: FixedU128 = FixedU128::from_rational(1, 1000); // 0.001
+}
+
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
@@ -240,6 +255,9 @@ pub mod pallet {
 
 	#[pallet::hooks]
 	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
+		/// Handles actually sending upward messages by moving them from `PendingUpwardMessages` to
+		/// `UpwardMessages`. Decreases the delivery fee factor if after sending messages, the queue
+		/// total size is less than the threshold (see [`ump_constants::THRESHOLD_FACTOR`]).
 		fn on_finalize(_: BlockNumberFor<T>) {
 			<DidSetValidationCode<T>>::kill();
 			<UpgradeRestrictionSignal<T>>::kill();
@@ -326,6 +344,17 @@ pub mod pallet {
 				UpwardMessages::<T>::put(&up[..num as usize]);
 				*up = up.split_off(num as usize);
 
+				// If the total size of the pending messages is less than the threshold,
+				// we decrease the fee factor, since the queue is less congested.
+				// This makes delivery of new messages cheaper.
+				let threshold = host_config
+					.max_upward_queue_size
+					.saturating_div(ump_constants::THRESHOLD_FACTOR);
+				let remaining_total_size: usize = up.iter().map(UpwardMessage::len).sum();
+				if remaining_total_size <= threshold as usize {
+					Self::decrease_fee_factor(());
+				}
+
 				(num, total_size)
 			});
 
@@ -721,7 +750,7 @@ pub mod pallet {
 		StorageValue<_, Vec<Ancestor<T::Hash>>, ValueQuery>;
 
 	/// Storage field that keeps track of bandwidth used by the unincluded segment along with the
-	/// latest the latest HRMP watermark. Used for limiting the acceptance of new blocks with
+	/// latest HRMP watermark. Used for limiting the acceptance of new blocks with
 	/// respect to relay chain constraints.
 	#[pallet::storage]
 	pub(super) type AggregatedUnincludedSegment<T: Config> =
@@ -860,6 +889,17 @@ pub mod pallet {
 	pub(super) type PendingUpwardMessages<T: Config> =
 		StorageValue<_, Vec<UpwardMessage>, ValueQuery>;
 
+	/// Initialization value for the delivery fee factor for UMP.
+	#[pallet::type_value]
+	pub fn UpwardInitialDeliveryFeeFactor() -> FixedU128 {
+		FixedU128::from_u32(1)
+	}
+
+	/// The factor to multiply the base delivery fee by for UMP.
+	#[pallet::storage]
+	pub(super) type UpwardDeliveryFeeFactor<T: Config> =
+		StorageValue<_, FixedU128, ValueQuery, UpwardInitialDeliveryFeeFactor>;
+
 	/// The number of HRMP messages we observed in `on_initialize` and thus used that number for
 	/// announcing the weight of `on_initialize` and `on_finalize`.
 	#[pallet::storage]
@@ -976,6 +1016,31 @@ impl<T: Config> Pallet<T> {
 	}
 }
 
+impl<T: Config> FeeTracker for Pallet<T> {
+	type Id = ();
+
+	fn get_fee_factor(_: Self::Id) -> FixedU128 {
+		UpwardDeliveryFeeFactor::<T>::get()
+	}
+
+	fn increase_fee_factor(_: Self::Id, message_size_factor: FixedU128) -> FixedU128 {
+		<UpwardDeliveryFeeFactor<T>>::mutate(|f| {
+			*f = f.saturating_mul(
+				ump_constants::EXPONENTIAL_FEE_BASE.saturating_add(message_size_factor),
+			);
+			*f
+		})
+	}
+
+	fn decrease_fee_factor(_: Self::Id) -> FixedU128 {
+		<UpwardDeliveryFeeFactor<T>>::mutate(|f| {
+			*f =
+				UpwardInitialDeliveryFeeFactor::get().max(*f / ump_constants::EXPONENTIAL_FEE_BASE);
+			*f
+		})
+	}
+}
+
 impl<T: Config> GetChannelInfo for Pallet<T> {
 	fn get_channel_status(id: ParaId) -> ChannelStatus {
 		// Note, that we are using `relevant_messaging_state` which may be from the previous
@@ -1468,7 +1533,13 @@ impl<T: Config> frame_system::SetCode<T> for ParachainSetCode<T> {
 }
 
 impl<T: Config> Pallet<T> {
+	/// Puts a message in the `PendingUpwardMessages` storage item.
+	/// The message will be later sent in `on_finalize`.
+	/// Checks host configuration to see if message is too big.
+	/// Increases the delivery fee factor if the queue is sufficiently (see
+	/// [`ump_constants::THRESHOLD_FACTOR`]) congested.
 	pub fn send_upward_message(message: UpwardMessage) -> Result<(u32, XcmHash), MessageSendError> {
+		let message_len = message.len();
 		// Check if the message fits into the relay-chain constraints.
 		//
 		// Note, that we are using `host_configuration` here which may be from the previous
@@ -1482,9 +1553,21 @@ impl<T: Config> Pallet<T> {
 		//
 		// However, changing this setting is expected to be rare.
 		if let Some(cfg) = Self::host_configuration() {
-			if message.len() > cfg.max_upward_message_size as usize {
+			if message_len > cfg.max_upward_message_size as usize {
 				return Err(MessageSendError::TooBig)
 			}
+			let threshold =
+				cfg.max_upward_queue_size.saturating_div(ump_constants::THRESHOLD_FACTOR);
+			// We check the threshold against total size and not number of messages since messages
+			// could be big or small.
+			let pending_messages = PendingUpwardMessages::<T>::get();
+			let total_size: usize = pending_messages.iter().map(UpwardMessage::len).sum();
+			if total_size > threshold as usize {
+				// We increase the fee factor by a factor based on the new message's size in KB
+				let message_size_factor = FixedU128::from((message_len / 1024) as u128)
+					.saturating_mul(ump_constants::MESSAGE_SIZE_FEE_BASE);
+				Self::increase_fee_factor((), message_size_factor);
+			}
 		} else {
 			// This storage field should carry over from the previous block. So if it's None
 			// then it must be that this is an edge-case where a message is attempted to be
@@ -1496,6 +1579,7 @@ impl<T: Config> Pallet<T> {
 			//
 			// Thus fall through here.
 		};
+
 		<PendingUpwardMessages<T>>::append(message.clone());
 
 		// The relay ump does not use using_encoded

cumulus/pallets/xcmp-queue/src/lib.rs

@@ -47,7 +47,7 @@ use frame_support::{
 	traits::{EnsureOrigin, Get},
 	weights::{constants::WEIGHT_REF_TIME_PER_MILLIS, Weight},
 };
-use polkadot_runtime_common::xcm_sender::PriceForParachainDelivery;
+use polkadot_runtime_common::xcm_sender::PriceForMessageDelivery;
 use polkadot_runtime_parachains::FeeTracker;
 use rand_chacha::{
 	rand_core::{RngCore, SeedableRng},
@@ -110,7 +110,7 @@ pub mod pallet {
 		type ControllerOriginConverter: ConvertOrigin<Self::RuntimeOrigin>;
 
 		/// The price for delivering an XCM to a sibling parachain destination.
-		type PriceForSiblingDelivery: PriceForParachainDelivery;
+		type PriceForSiblingDelivery: PriceForMessageDelivery<Id = ParaId>;
 
 		/// The weight information of this pallet.
 		type WeightInfo: WeightInfo;
@@ -970,28 +970,6 @@ impl<T: Config> Pallet<T> {
 			}
 		});
 	}
-
-	/// Increases the delivery fee factor by a multiplicative factor and stores the resulting value.
-	///
-	/// Returns the new delivery fee factor after the increase.
-	pub(crate) fn increase_fee_factor(para: ParaId, message_size_factor: FixedU128) -> FixedU128 {
-		<DeliveryFeeFactor<T>>::mutate(para, |f| {
-			*f = f.saturating_mul(EXPONENTIAL_FEE_BASE.saturating_add(message_size_factor));
-			*f
-		})
-	}
-
-	/// Decreases the delivery fee factor by a multiplicative factor and stores the resulting value.
-	///
-	/// Does not reduce the fee factor below the initial value, which is currently set as 1.
-	///
-	/// Returns the new delivery fee factor after the decrease.
-	pub(crate) fn decrease_fee_factor(para: ParaId) -> FixedU128 {
-		<DeliveryFeeFactor<T>>::mutate(para, |f| {
-			*f = InitialFactor::get().max(*f / EXPONENTIAL_FEE_BASE);
-			*f
-		})
-	}
 }
 
 impl<T: Config> XcmpMessageHandler for Pallet<T> {
@@ -1203,7 +1181,7 @@ impl<T: Config> SendXcm for Pallet<T> {
 			MultiLocation { parents: 1, interior: X1(Parachain(id)) } => {
 				let xcm = msg.take().ok_or(SendError::MissingArgument)?;
 				let id = ParaId::from(*id);
-				let price = T::PriceForSiblingDelivery::price_for_parachain_delivery(id, &xcm);
+				let price = T::PriceForSiblingDelivery::price_for_delivery(id, &xcm);
 				let versioned_xcm = T::VersionWrapper::wrap_version(&d, xcm)
 					.map_err(|()| SendError::DestinationUnsupported)?;
 				Ok(((id, versioned_xcm), price))
@@ -1231,7 +1209,23 @@ impl<T: Config> SendXcm for Pallet<T> {
 }
 
 impl<T: Config> FeeTracker for Pallet<T> {
-	fn get_fee_factor(para: ParaId) -> FixedU128 {
-		<DeliveryFeeFactor<T>>::get(para)
+	type Id = ParaId;
+
+	fn get_fee_factor(id: Self::Id) -> FixedU128 {
+		<DeliveryFeeFactor<T>>::get(id)
+	}
+
+	fn increase_fee_factor(id: Self::Id, message_size_factor: FixedU128) -> FixedU128 {
+		<DeliveryFeeFactor<T>>::mutate(id, |f| {
+			*f = f.saturating_mul(EXPONENTIAL_FEE_BASE.saturating_add(message_size_factor));
+			*f
+		})
+	}
+
+	fn decrease_fee_factor(id: Self::Id) -> FixedU128 {
+		<DeliveryFeeFactor<T>>::mutate(id, |f| {
+			*f = InitialFactor::get().max(*f / EXPONENTIAL_FEE_BASE);
+			*f
+		})
 	}
 }

cumulus/pallets/xcmp-queue/src/mock.rs

@@ -23,6 +23,7 @@ use frame_support::{
 	traits::{ConstU32, Everything, Nothing, OriginTrait},
 };
 use frame_system::EnsureRoot;
+use polkadot_runtime_common::xcm_sender::NoPriceForMessageDelivery;
 use sp_core::H256;
 use sp_runtime::{
 	traits::{BlakeTwo256, IdentityLookup},
@@ -205,7 +206,7 @@ impl Config for Test {
 	type ControllerOrigin = EnsureRoot<AccountId>;
 	type ControllerOriginConverter = SystemParachainAsSuperuser<RuntimeOrigin>;
 	type WeightInfo = ();
-	type PriceForSiblingDelivery = ();
+	type PriceForSiblingDelivery = NoPriceForMessageDelivery<ParaId>;
 }
 
 pub fn new_test_ext() -> sp_io::TestExternalities {

cumulus/parachain-template/runtime/src/lib.rs

@@ -10,6 +10,8 @@ mod weights;
 pub mod xcm_config;
 
 use cumulus_pallet_parachain_system::RelayNumberStrictlyIncreases;
+use cumulus_primitives_core::ParaId;
+use polkadot_runtime_common::xcm_sender::NoPriceForMessageDelivery;
 use smallvec::smallvec;
 use sp_api::impl_runtime_apis;
 use sp_core::{crypto::KeyTypeId, OpaqueMetadata};
@@ -412,7 +414,7 @@ impl cumulus_pallet_xcmp_queue::Config for Runtime {
 	type ControllerOrigin = EnsureRoot<AccountId>;
 	type ControllerOriginConverter = XcmOriginToTransactDispatchOrigin;
 	type WeightInfo = ();
-	type PriceForSiblingDelivery = ();
+	type PriceForSiblingDelivery = NoPriceForMessageDelivery<ParaId>;
 }
 
 impl cumulus_pallet_dmp_queue::Config for Runtime {

cumulus/parachains/integration-tests/emulated/assets/asset-hub-westend/Cargo.toml

@@ -31,6 +31,7 @@ xcm-builder = { package = "staging-xcm-builder",  path = "../../../../../../polk
 xcm-executor = { package = "staging-xcm-executor",  path = "../../../../../../polkadot/xcm/xcm-executor", default-features = false}
 pallet-xcm = { path = "../../../../../../polkadot/xcm/pallet-xcm", default-features = false}
 westend-runtime = { path = "../../../../../../polkadot/runtime/westend", default-features = false }
+westend-runtime-constants = { path = "../../../../../../polkadot/runtime/westend/constants", default-features = false }
 
 # Cumulus
 parachains-common = { path = "../../../../common" }