Rework Transaction Priority calculation (#9834)

* Add transaction validity docs.

* Re-work priority calculation.

* Fix tests.

* Update frame/transaction-payment/src/lib.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* cargo +nightly fmt --all

* Fix an obvious mistake :)

* Re-work again.

* Fix test.

* cargo +nightly fmt --all

* Make VirtualTip dependent on the transaction size.

* cargo +nightly fmt --all

* Update frame/transaction-payment/src/lib.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Fix compilation.

* Update bin/node/runtime/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/Cargo.lock

@@ -2473,9 +2473,9 @@ dependencies = [
 
 [[package]]
 name = "git2"
-version = "0.13.21"
+version = "0.13.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "659cd14835e75b64d9dba5b660463506763cf0aa6cb640aeeb0e98d841093490"
+checksum = "9c1cbbfc9a1996c6af82c2b4caf828d2c653af4fcdbb0e5674cc966eee5a4197"
 dependencies = [
  "bitflags",
  "libc",
@@ -3294,9 +3294,9 @@ checksum = "789da6d93f1b866ffe175afc5322a4d76c038605a1c3319bb57b06967ca98a36"
 
 [[package]]
 name = "libgit2-sys"
-version = "0.12.22+1.1.0"
+version = "0.12.23+1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "89c53ac117c44f7042ad8d8f5681378dfbc6010e49ec2c0d1f11dfedc7a4a1c3"
+checksum = "29730a445bae719db3107078b46808cc45a5b7a6bae3f31272923af969453356"
 dependencies = [
  "cc",
  "libc",

substrate/bin/node-template/runtime/src/lib.rs

@@ -258,11 +258,13 @@ impl pallet_balances::Config for Runtime {
 
 parameter_types! {
 	pub const TransactionByteFee: Balance = 1;
+	pub OperationalFeeMultiplier: u8 = 5;
 }
 
 impl pallet_transaction_payment::Config for Runtime {
 	type OnChargeTransaction = CurrencyAdapter<Balances, ()>;
 	type TransactionByteFee = TransactionByteFee;
+	type OperationalFeeMultiplier = OperationalFeeMultiplier;
 	type WeightToFee = IdentityFee<Balance>;
 	type FeeMultiplierUpdate = ();
 }

substrate/bin/node/runtime/src/lib.rs

@@ -413,6 +413,7 @@ impl pallet_balances::Config for Runtime {
 
 parameter_types! {
 	pub const TransactionByteFee: Balance = 10 * MILLICENTS;
+	pub const OperationalFeeMultiplier: u8 = 5;
 	pub const TargetBlockFullness: Perquintill = Perquintill::from_percent(25);
 	pub AdjustmentVariable: Multiplier = Multiplier::saturating_from_rational(1, 100_000);
 	pub MinimumMultiplier: Multiplier = Multiplier::saturating_from_rational(1, 1_000_000_000u128);
@@ -421,6 +422,7 @@ parameter_types! {
 impl pallet_transaction_payment::Config for Runtime {
 	type OnChargeTransaction = CurrencyAdapter<Balances, DealWithFees>;
 	type TransactionByteFee = TransactionByteFee;
+	type OperationalFeeMultiplier = OperationalFeeMultiplier;
 	type WeightToFee = IdentityFee<Balance>;
 	type FeeMultiplierUpdate =
 		TargetedFeeAdjustment<Self, TargetBlockFullness, AdjustmentVariable, MinimumMultiplier>;

substrate/frame/balances/src/tests_composite.rs

@@ -76,10 +76,12 @@ impl frame_system::Config for Test {
 }
 parameter_types! {
 	pub const TransactionByteFee: u64 = 1;
+	pub const OperationalFeeMultiplier: u8 = 5;
 }
 impl pallet_transaction_payment::Config for Test {
 	type OnChargeTransaction = CurrencyAdapter<Pallet<Test>, ()>;
 	type TransactionByteFee = TransactionByteFee;
+	type OperationalFeeMultiplier = OperationalFeeMultiplier;
 	type WeightToFee = IdentityFee<u64>;
 	type FeeMultiplierUpdate = ();
 }

substrate/frame/balances/src/tests_local.rs

@@ -78,10 +78,12 @@ impl frame_system::Config for Test {
 }
 parameter_types! {
 	pub const TransactionByteFee: u64 = 1;
+	pub const OperationalFeeMultiplier: u8 = 5;
 }
 impl pallet_transaction_payment::Config for Test {
 	type OnChargeTransaction = CurrencyAdapter<Pallet<Test>, ()>;
 	type TransactionByteFee = TransactionByteFee;
+	type OperationalFeeMultiplier = OperationalFeeMultiplier;
 	type WeightToFee = IdentityFee<u64>;
 	type FeeMultiplierUpdate = ();
 }

substrate/frame/balances/src/tests_reentrancy.rs

@@ -80,10 +80,12 @@ impl frame_system::Config for Test {
 }
 parameter_types! {
 	pub const TransactionByteFee: u64 = 1;
+	pub const OperationalFeeMultiplier: u8 = 5;
 }
 impl pallet_transaction_payment::Config for Test {
 	type OnChargeTransaction = CurrencyAdapter<Pallet<Test>, ()>;
 	type TransactionByteFee = TransactionByteFee;
+	type OperationalFeeMultiplier = OperationalFeeMultiplier;
 	type WeightToFee = IdentityFee<u64>;
 	type FeeMultiplierUpdate = ();
 }

substrate/frame/executive/src/lib.rs

@@ -800,10 +800,12 @@ mod tests {
 
 	parameter_types! {
 		pub const TransactionByteFee: Balance = 0;
+		pub const OperationalFeeMultiplier: u8 = 5;
 	}
 	impl pallet_transaction_payment::Config for Runtime {
 		type OnChargeTransaction = CurrencyAdapter<Balances, ()>;
 		type TransactionByteFee = TransactionByteFee;
+		type OperationalFeeMultiplier = OperationalFeeMultiplier;
 		type WeightToFee = IdentityFee<Balance>;
 		type FeeMultiplierUpdate = ();
 	}
@@ -1110,8 +1112,6 @@ mod tests {
 		let invalid = TestXt::new(Call::Custom(custom::Call::unallowed_unsigned {}), None);
 		let mut t = new_test_ext(1);
 
-		let mut default_with_prio_3 = ValidTransaction::default();
-		default_with_prio_3.priority = 3;
 		t.execute_with(|| {
 			assert_eq!(
 				Executive::validate_transaction(
@@ -1119,7 +1119,7 @@ mod tests {
 					valid.clone(),
 					Default::default(),
 				),
-				Ok(default_with_prio_3),
+				Ok(ValidTransaction::default()),
 			);
 			assert_eq!(
 				Executive::validate_transaction(

substrate/frame/support/src/weights.rs

@@ -287,30 +287,6 @@ impl<'a> OneOrMany<DispatchClass> for &'a [DispatchClass] {
 	}
 }
 
-/// Primitives related to priority management of Frame.
-pub mod priority {
-	/// The starting point of all Operational transactions. 3/4 of u64::MAX.
-	pub const LIMIT: u64 = 13_835_058_055_282_163_711_u64;
-
-	/// Wrapper for priority of different dispatch classes.
-	///
-	/// This only makes sure that any value created for the operational dispatch class is
-	/// incremented by [`LIMIT`].
-	pub enum FrameTransactionPriority {
-		Normal(u64),
-		Operational(u64),
-	}
-
-	impl From<FrameTransactionPriority> for u64 {
-		fn from(priority: FrameTransactionPriority) -> Self {
-			match priority {
-				FrameTransactionPriority::Normal(inner) => inner,
-				FrameTransactionPriority::Operational(inner) => inner.saturating_add(LIMIT),
-			}
-		}
-	}
-}
-
 /// A bundle of static information collected from the `#[weight = $x]` attributes.
 #[derive(Clone, Copy, Eq, PartialEq, Default, RuntimeDebug, Encode, Decode, TypeInfo)]
 pub struct DispatchInfo {

substrate/frame/system/src/extensions/check_genesis.rs

@@ -24,6 +24,11 @@ use sp_runtime::{
 };
 
 /// Genesis hash check to provide replay protection between different networks.
+///
+/// # Transaction Validity
+///
+/// Note that while a transaction with invalid `genesis_hash` will fail to be decoded,
+/// the extension does not affect any other fields of `TransactionValidity` directly.
 #[derive(Encode, Decode, Clone, Eq, PartialEq, TypeInfo)]
 #[scale_info(skip_type_params(T))]
 pub struct CheckGenesis<T: Config + Send + Sync>(sp_std::marker::PhantomData<T>);

substrate/frame/system/src/extensions/check_mortality.rs

@@ -27,6 +27,10 @@ use sp_runtime::{
 };
 
 /// Check for transaction mortality.
+///
+/// # Transaction Validity
+///
+/// The extension affects `longevity` of the transaction according to the [`Era`] definition.
 #[derive(Encode, Decode, Clone, Eq, PartialEq, TypeInfo)]
 #[scale_info(skip_type_params(T))]
 pub struct CheckMortality<T: Config + Send + Sync>(Era, sp_std::marker::PhantomData<T>);

substrate/frame/system/src/extensions/check_nonce.rs

@@ -30,8 +30,11 @@ use sp_std::vec;
 
 /// Nonce check and increment to give replay protection for transactions.
 ///
-/// Note that this does not set any priority by default. Make sure that AT LEAST one of the signed
-/// extension sets some kind of priority upon validating transactions.
+/// # Transaction Validity
+///
+/// This extension affects `requires` and `provides` tags of validity, but DOES NOT
+/// set the `priority` field. Make sure that AT LEAST one of the signed extension sets
+/// some kind of priority upon validating transactions.
 #[derive(Encode, Decode, Clone, Eq, PartialEq, TypeInfo)]
 #[scale_info(skip_type_params(T))]
 pub struct CheckNonce<T: Config>(#[codec(compact)] pub T::Index);

substrate/frame/system/src/extensions/check_spec_version.rs

@@ -21,6 +21,11 @@ use scale_info::TypeInfo;
 use sp_runtime::{traits::SignedExtension, transaction_validity::TransactionValidityError};
 
 /// Ensure the runtime version registered in the transaction is the same as at present.
+///
+/// # Transaction Validity
+///
+/// The transaction with incorrect `spec_version` are considered invalid. The validity
+/// is not affected in any other way.
 #[derive(Encode, Decode, Clone, Eq, PartialEq, TypeInfo)]
 #[scale_info(skip_type_params(T))]
 pub struct CheckSpecVersion<T: Config + Send + Sync>(sp_std::marker::PhantomData<T>);

substrate/frame/system/src/extensions/check_tx_version.rs

@@ -21,6 +21,11 @@ use scale_info::TypeInfo;
 use sp_runtime::{traits::SignedExtension, transaction_validity::TransactionValidityError};
 
 /// Ensure the transaction version registered in the transaction is the same as at present.
+///
+/// # Transaction Validity
+///
+/// The transaction with incorrect `transaction_version` are considered invalid. The validity
+/// is not affected in any other way.
 #[derive(Encode, Decode, Clone, Eq, PartialEq, TypeInfo)]
 #[scale_info(skip_type_params(T))]
 pub struct CheckTxVersion<T: Config + Send + Sync>(sp_std::marker::PhantomData<T>);

substrate/frame/system/src/extensions/check_weight.rs

@@ -19,19 +19,21 @@ use crate::{limits::BlockWeights, Config, Pallet};
 use codec::{Decode, Encode};
 use frame_support::{
 	traits::Get,
-	weights::{priority::FrameTransactionPriority, DispatchClass, DispatchInfo, PostDispatchInfo},
+	weights::{DispatchClass, DispatchInfo, PostDispatchInfo},
 };
 use scale_info::TypeInfo;
 use sp_runtime::{
 	traits::{DispatchInfoOf, Dispatchable, PostDispatchInfoOf, SignedExtension},
-	transaction_validity::{
-		InvalidTransaction, TransactionPriority, TransactionValidity, TransactionValidityError,
-		ValidTransaction,
-	},
+	transaction_validity::{InvalidTransaction, TransactionValidity, TransactionValidityError},
 	DispatchResult,
 };
 
 /// Block resource (weight) limit check.
+///
+/// # Transaction Validity
+///
+/// This extension does not influence any fields of `TransactionValidity` in case the
+/// transaction is valid.
 #[derive(Encode, Decode, Clone, Eq, PartialEq, Default, TypeInfo)]
 #[scale_info(skip_type_params(T))]
 pub struct CheckWeight<T: Config + Send + Sync>(sp_std::marker::PhantomData<T>);
@@ -81,23 +83,6 @@ where
 		}
 	}
 
-	/// Get the priority of an extrinsic denoted by `info`.
-	///
-	/// Operational transaction will be given a fixed initial amount to be fairly distinguished from
-	/// the normal ones.
-	fn get_priority(info: &DispatchInfoOf<T::Call>) -> TransactionPriority {
-		match info.class {
-			// Normal transaction.
-			DispatchClass::Normal => FrameTransactionPriority::Normal(info.weight.into()).into(),
-			// Don't use up the whole priority space, to allow things like `tip` to be taken into
-			// account as well.
-			DispatchClass::Operational =>
-				FrameTransactionPriority::Operational(info.weight.into()).into(),
-			// Mandatory extrinsics are only for inherents; never transactions.
-			DispatchClass::Mandatory => TransactionPriority::min_value(),
-		}
-	}
-
 	/// Creates new `SignedExtension` to check weight of the extrinsic.
 	pub fn new() -> Self {
 		Self(Default::default())
@@ -130,7 +115,7 @@ where
 		// consumption from causing false negatives.
 		Self::check_extrinsic_weight(info)?;
 
-		Ok(ValidTransaction { priority: Self::get_priority(info), ..Default::default() })
+		Ok(Default::default())
 	}
 }
 
@@ -368,13 +353,7 @@ mod tests {
 			};
 			let len = 0_usize;
 
-			assert_eq!(
-				CheckWeight::<Test>::do_validate(&okay, len),
-				Ok(ValidTransaction {
-					priority: CheckWeight::<Test>::get_priority(&okay),
-					..Default::default()
-				})
-			);
+			assert_eq!(CheckWeight::<Test>::do_validate(&okay, len), Ok(Default::default()));
 			assert_err!(
 				CheckWeight::<Test>::do_validate(&max, len),
 				InvalidTransaction::ExhaustsResources
@@ -506,30 +485,6 @@ mod tests {
 		})
 	}
 
-	#[test]
-	fn signed_ext_check_weight_works() {
-		new_test_ext().execute_with(|| {
-			let normal =
-				DispatchInfo { weight: 100, class: DispatchClass::Normal, pays_fee: Pays::Yes };
-			let op = DispatchInfo {
-				weight: 100,
-				class: DispatchClass::Operational,
-				pays_fee: Pays::Yes,
-			};
-			let len = 0_usize;
-
-			let priority = CheckWeight::<Test>(PhantomData)
-				.validate(&1, CALL, &normal, len)
-				.unwrap()
-				.priority;
-			assert_eq!(priority, 100);
-
-			let priority =
-				CheckWeight::<Test>(PhantomData).validate(&1, CALL, &op, len).unwrap().priority;
-			assert_eq!(priority, frame_support::weights::priority::LIMIT + 100);
-		})
-	}
-
 	#[test]
 	fn signed_ext_check_weight_block_size_works() {
 		new_test_ext().execute_with(|| {

substrate/frame/transaction-payment/src/lib.rs

@@ -264,6 +264,30 @@ pub mod pallet {
 		#[pallet::constant]
 		type TransactionByteFee: Get<BalanceOf<Self>>;
 
+		/// A fee mulitplier for `Operational` extrinsics to compute "virtual tip" to boost their
+		/// `priority`
+		///
+		/// This value is multipled by the `final_fee` to obtain a "virtual tip" that is later
+		/// added to a tip component in regular `priority` calculations.
+		/// It means that a `Normal` transaction can front-run a similarly-sized `Operational`
+		/// extrinsic (with no tip), by including a tip value greater than the virtual tip.
+		///
+		/// ```rust,ignore
+		/// // For `Normal`
+		/// let priority = priority_calc(tip);
+		///
+		/// // For `Operational`
+		/// let virtual_tip = (inclusion_fee + tip) * OperationalFeeMultiplier;
+		/// let priority = priority_calc(tip + virtual_tip);
+		/// ```
+		///
+		/// Note that since we use `final_fee` the multiplier applies also to the regular `tip`
+		/// sent with the transaction. So, not only does the transaction get a priority bump based
+		/// on the `inclusion_fee`, but we also amplify the impact of tips applied to `Operational`
+		/// transactions.
+		#[pallet::constant]
+		type OperationalFeeMultiplier: Get<u8>;
+
 		/// Convert a weight value into a deductible fee based on the currency type.
 		type WeightToFee: WeightToFeePolynomial<Balance = BalanceOf<Self>>;
 
@@ -525,6 +549,14 @@ where
 
 /// Require the transactor pay for themselves and maybe include a tip to gain additional priority
 /// in the queue.
+///
+/// # Transaction Validity
+///
+/// This extension sets the `priority` field of `TransactionValidity` depending on the amount
+/// of tip being paid per weight unit.
+///
+/// Operational transactions will receive an additional priority bump, so that they are normally
+/// considered before regular transactions.
 #[derive(Encode, Decode, Clone, Eq, PartialEq, TypeInfo)]
 #[scale_info(skip_type_params(T))]
 pub struct ChargeTransactionPayment<T: Config>(#[codec(compact)] BalanceOf<T>);
@@ -566,27 +598,73 @@ where
 		.map(|i| (fee, i))
 	}
 
-	/// Get an appropriate priority for a transaction with the given length and info.
+	/// Get an appropriate priority for a transaction with the given `DispatchInfo`, encoded length
+	/// and user-included tip.
 	///
-	/// This will try and optimise the `fee/weight` `fee/length`, whichever is consuming more of the
-	/// maximum corresponding limit.
+	/// The priority is based on the amount of `tip` the user is willing to pay per unit of either
+	/// `weight` or `length`, depending which one is more limitting. For `Operational` extrinsics
+	/// we add a "virtual tip" to the calculations.
 	///
-	/// For example, if a transaction consumed 1/4th of the block length and half of the weight, its
-	/// final priority is `fee * min(2, 4) = fee * 2`. If it consumed `1/4th` of the block length
-	/// and the entire block weight `(1/1)`, its priority is `fee * min(1, 4) = fee * 1`. This means
-	///  that the transaction which consumes more resources (either length or weight) with the same
-	/// `fee` ends up having lower priority.
-	fn get_priority(
-		len: usize,
+	/// The formula should simply be `tip / bounded_{weight|length}`, but since we are using
+	/// integer division, we have no guarantees it's going to give results in any reasonable
+	/// range (might simply end up being zero). Hence we use a scaling factor:
+	/// `tip * (max_block_{weight|length} / bounded_{weight|length})`, since given current
+	/// state of-the-art blockchains, number of per-block transactions is expected to be in a
+	/// range reasonable enough to not saturate the `Balance` type while multiplying by the tip.
+	pub fn get_priority(
 		info: &DispatchInfoOf<T::Call>,
+		len: usize,
+		tip: BalanceOf<T>,
 		final_fee: BalanceOf<T>,
 	) -> TransactionPriority {
-		let weight_saturation = T::BlockWeights::get().max_block / info.weight.max(1);
-		let max_block_length = *T::BlockLength::get().max.get(DispatchClass::Normal);
-		let len_saturation = max_block_length as u64 / (len as u64).max(1);
-		let coefficient: BalanceOf<T> =
-			weight_saturation.min(len_saturation).saturated_into::<BalanceOf<T>>();
-		final_fee.saturating_mul(coefficient).saturated_into::<TransactionPriority>()
+		// Calculate how many such extrinsics we could fit into an empty block and take
+		// the limitting factor.
+		let max_block_weight = T::BlockWeights::get().max_block;
+		let max_block_length = *T::BlockLength::get().max.get(info.class) as u64;
+
+		let bounded_weight = info.weight.max(1).min(max_block_weight);
+		let bounded_length = (len as u64).max(1).min(max_block_length);
+
+		let max_tx_per_block_weight = max_block_weight / bounded_weight;
+		let max_tx_per_block_length = max_block_length / bounded_length;
+		// Given our current knowledge this value is going to be in a reasonable range - i.e.
+		// less than 10^9 (2^30), so multiplying by the `tip` value is unlikely to overflow the
+		// balance type. We still use saturating ops obviously, but the point is to end up with some
+		// `priority` distribution instead of having all transactions saturate the priority.
+		let max_tx_per_block = max_tx_per_block_length
+			.min(max_tx_per_block_weight)
+			.saturated_into::<BalanceOf<T>>();
+		let max_reward = |val: BalanceOf<T>| val.saturating_mul(max_tx_per_block);
+
+		// To distribute no-tip transactions a little bit, we set the minimal tip as `1`.
+		// This means that given two transactions without a tip, smaller one will be preferred.
+		let tip = tip.max(1.saturated_into());
+		let scaled_tip = max_reward(tip);
+
+		match info.class {
+			DispatchClass::Normal => {
+				// For normal class we simply take the `tip_per_weight`.
+				scaled_tip
+			},
+			DispatchClass::Mandatory => {
+				// Mandatory extrinsics should be prohibited (e.g. by the [`CheckWeight`]
+				// extensions), but just to be safe let's return the same priority as `Normal` here.
+				scaled_tip
+			},
+			DispatchClass::Operational => {
+				// A "virtual tip" value added to an `Operational` extrinsic.
+				// This value should be kept high enough to allow `Operational` extrinsics
+				// to get in even during congestion period, but at the same time low
+				// enough to prevent a possible spam attack by sending invalid operational
+				// extrinsics which push away regular transactions from the pool.
+				let fee_multiplier = T::OperationalFeeMultiplier::get().saturated_into();
+				let virtual_tip = final_fee.saturating_mul(fee_multiplier);
+				let scaled_virtual_tip = max_reward(virtual_tip);
+
+				scaled_tip.saturating_add(scaled_virtual_tip)
+			},
+		}
+		.saturated_into::<TransactionPriority>()
 	}
 }
 
@@ -629,8 +707,12 @@ where
 		info: &DispatchInfoOf<Self::Call>,
 		len: usize,
 	) -> TransactionValidity {
-		let (fee, _) = self.withdraw_fee(who, call, info, len)?;
-		Ok(ValidTransaction { priority: Self::get_priority(len, info, fee), ..Default::default() })
+		let (final_fee, _) = self.withdraw_fee(who, call, info, len)?;
+		let tip = self.0;
+		Ok(ValidTransaction {
+			priority: Self::get_priority(info, len, tip, final_fee),
+			..Default::default()
+		})
 	}
 
 	fn pre_dispatch(
@@ -743,6 +825,7 @@ mod tests {
 		pub const BlockHashCount: u64 = 250;
 		pub static TransactionByteFee: u64 = 1;
 		pub static WeightToFee: u64 = 1;
+		pub static OperationalFeeMultiplier: u8 = 5;
 	}
 
 	impl frame_system::Config for Runtime {
@@ -822,6 +905,7 @@ mod tests {
 	impl Config for Runtime {
 		type OnChargeTransaction = CurrencyAdapter<Balances, DealWithFees>;
 		type TransactionByteFee = TransactionByteFee;
+		type OperationalFeeMultiplier = OperationalFeeMultiplier;
 		type WeightToFee = WeightToFee;
 		type FeeMultiplierUpdate = ();
 	}
@@ -1335,6 +1419,79 @@ mod tests {
 			});
 	}
 
+	#[test]
+	fn should_alter_operational_priority() {
+		let tip = 5;
+		let len = 10;
+
+		ExtBuilder::default().balance_factor(100).build().execute_with(|| {
+			let normal =
+				DispatchInfo { weight: 100, class: DispatchClass::Normal, pays_fee: Pays::Yes };
+			let priority = ChargeTransactionPayment::<Runtime>(tip)
+				.validate(&2, CALL, &normal, len)
+				.unwrap()
+				.priority;
+
+			assert_eq!(priority, 50);
+
+			let priority = ChargeTransactionPayment::<Runtime>(2 * tip)
+				.validate(&2, CALL, &normal, len)
+				.unwrap()
+				.priority;
+
+			assert_eq!(priority, 100);
+		});
+
+		ExtBuilder::default().balance_factor(100).build().execute_with(|| {
+			let op = DispatchInfo {
+				weight: 100,
+				class: DispatchClass::Operational,
+				pays_fee: Pays::Yes,
+			};
+			let priority = ChargeTransactionPayment::<Runtime>(tip)
+				.validate(&2, CALL, &op, len)
+				.unwrap()
+				.priority;
+			assert_eq!(priority, 5800);
+
+			let priority = ChargeTransactionPayment::<Runtime>(2 * tip)
+				.validate(&2, CALL, &op, len)
+				.unwrap()
+				.priority;
+			assert_eq!(priority, 6100);
+		});
+	}
+
+	#[test]
+	fn no_tip_has_some_priority() {
+		let tip = 0;
+		let len = 10;
+
+		ExtBuilder::default().balance_factor(100).build().execute_with(|| {
+			let normal =
+				DispatchInfo { weight: 100, class: DispatchClass::Normal, pays_fee: Pays::Yes };
+			let priority = ChargeTransactionPayment::<Runtime>(tip)
+				.validate(&2, CALL, &normal, len)
+				.unwrap()
+				.priority;
+
+			assert_eq!(priority, 10);
+		});
+
+		ExtBuilder::default().balance_factor(100).build().execute_with(|| {
+			let op = DispatchInfo {
+				weight: 100,
+				class: DispatchClass::Operational,
+				pays_fee: Pays::Yes,
+			};
+			let priority = ChargeTransactionPayment::<Runtime>(tip)
+				.validate(&2, CALL, &op, len)
+				.unwrap()
+				.priority;
+			assert_eq!(priority, 5510);
+		});
+	}
+
 	#[test]
 	fn post_info_can_change_pays_fee() {
 		ExtBuilder::default()