Implements a variable deposit base calculation for EPM signed submissions

bin/node/runtime/src/lib.rs

@@ -52,7 +52,7 @@ use frame_system::{
 };
 pub use node_primitives::{AccountId, Signature};
 use node_primitives::{AccountIndex, Balance, BlockNumber, Hash, Index, Moment};
-use pallet_election_provider_multi_phase::SolutionAccuracyOf;
+use pallet_election_provider_multi_phase::{GeometricDepositBase, SolutionAccuracyOf};
 use pallet_im_online::sr25519::AuthorityId as ImOnlineId;
 use pallet_nfts::PalletFeatures;
 use pallet_nis::WithMaximumOf;
@@ -621,7 +621,8 @@ parameter_types! {
 
 	// signed config
 	pub const SignedRewardBase: Balance = 1 * DOLLARS;
-	pub const SignedDepositBase: Balance = 1 * DOLLARS;
+	pub const SignedFixedDepositBase: Balance = 1 * DOLLARS;
+	pub const SignedDepositBaseIncreaseFactor: Percent = Percent::from_percent(10);
 	pub const SignedDepositByte: Balance = 1 * CENTS;
 
 	pub BetterUnsignedThreshold: Perbill = Perbill::from_rational(1u32, 10_000);
@@ -747,7 +748,9 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type MinerConfig = Self;
 	type SignedMaxSubmissions = ConstU32<10>;
 	type SignedRewardBase = SignedRewardBase;
-	type SignedDepositBase = SignedDepositBase;
+	type SignedDepositBase = GeometricDepositBase<Runtime>;
+	type SignedFixedDepositBase = SignedFixedDepositBase;
+	type SignedDepositBaseIncreaseFactor = SignedDepositBaseIncreaseFactor;
 	type SignedDepositByte = SignedDepositByte;
 	type SignedMaxRefunds = ConstU32<3>;
 	type SignedDepositWeight = ();

frame/election-provider-multi-phase/src/lib.rs

@@ -253,7 +253,7 @@ use sp_runtime::{
 		InvalidTransaction, TransactionPriority, TransactionSource, TransactionValidity,
 		TransactionValidityError, ValidTransaction,
 	},
-	DispatchError, ModuleError, PerThing, Perbill, RuntimeDebug, SaturatedConversion,
+	DispatchError, ModuleError, PerThing, Perbill, Percent, RuntimeDebug, SaturatedConversion,
 };
 use sp_std::prelude::*;
 
@@ -274,8 +274,8 @@ use unsigned::VoterOf;
 pub use weights::WeightInfo;
 
 pub use signed::{
-	BalanceOf, NegativeImbalanceOf, PositiveImbalanceOf, SignedSubmission, SignedSubmissionOf,
-	SignedSubmissions, SubmissionIndicesOf,
+	BalanceOf, GeometricDepositBase, NegativeImbalanceOf, PositiveImbalanceOf, SignedSubmission,
+	SignedSubmissionOf, SignedSubmissions, SubmissionIndicesOf,
 };
 pub use unsigned::{Miner, MinerConfig};
 
@@ -567,6 +567,7 @@ pub mod pallet {
 	use frame_election_provider_support::{InstantElectionProvider, NposSolver};
 	use frame_support::{pallet_prelude::*, traits::EstimateCallFee};
 	use frame_system::pallet_prelude::*;
+	use sp_runtime::traits::Convert;
 
 	#[pallet::config]
 	pub trait Config: frame_system::Config + SendTransactionTypes<Call<Self>> {
@@ -644,9 +645,16 @@ pub mod pallet {
 		#[pallet::constant]
 		type SignedRewardBase: Get<BalanceOf<Self>>;
 
-		/// Base deposit for a signed solution.
+		/// Fixed base deposit for a signed solution.
 		#[pallet::constant]
-		type SignedDepositBase: Get<BalanceOf<Self>>;
+		type SignedFixedDepositBase: Get<BalanceOf<Self>>;
+
+		/// Increase factor of the geometric series for the base deposit computation.
+		///
+		/// If 0, then signed base deposit remains constant regardless of the submissions queue size
+		/// (and equal to `SignedFixedDepositBase`).
+		#[pallet::constant]
+		type SignedDepositBaseIncreaseFactor: Get<Percent>;
 
 		/// Per-byte deposit for a signed solution.
 		#[pallet::constant]
@@ -673,6 +681,10 @@ pub mod pallet {
 		#[pallet::constant]
 		type MaxWinners: Get<u32>;
 
+		/// Something that calculates the signed deposit base based on the signed submissions queue
+		/// size.
+		type SignedDepositBase: Convert<usize, BalanceOf<Self>>;
+
 		/// Handler for the slashed deposits.
 		type SlashHandler: OnUnbalanced<NegativeImbalanceOf<Self>>;
 

frame/election-provider-multi-phase/src/mock.rs

@@ -16,7 +16,7 @@
 // limitations under the License.
 
 use super::*;
-use crate::{self as multi_phase, unsigned::MinerConfig};
+use crate::{self as multi_phase, signed::GeometricDepositBase, unsigned::MinerConfig};
 use frame_election_provider_support::{
 	data_provider,
 	onchain::{self},
@@ -44,7 +44,7 @@ use sp_npos_elections::{
 };
 use sp_runtime::{
 	testing::Header,
-	traits::{BlakeTwo256, IdentityLookup},
+	traits::{BlakeTwo256, Convert, IdentityLookup},
 	PerU16,
 };
 use std::sync::Arc;
@@ -287,7 +287,11 @@ parameter_types! {
 	pub static UnsignedPhase: BlockNumber = 5;
 	pub static SignedMaxSubmissions: u32 = 5;
 	pub static SignedMaxRefunds: u32 = 1;
-	pub static SignedDepositBase: Balance = 5;
+	// for tests only. if `EnableVariableDepositBase` is true, the deposit base will be calculated
+	// by `Multiphase::DepositBase`. Otherwise the deposit base is `SignedFixedDepositBase`.
+	pub static EnableVariableDepositBase: bool = false;
+	pub static SignedFixedDepositBase: Balance = 5;
+	pub static SignedDepositBaseIncreaseFactor: Percent = Percent::from_percent(10);
 	pub static SignedDepositByte: Balance = 0;
 	pub static SignedDepositWeight: Balance = 0;
 	pub static SignedRewardBase: Balance = 7;
@@ -393,7 +397,9 @@ impl crate::Config for Runtime {
 	type OffchainRepeat = OffchainRepeat;
 	type MinerTxPriority = MinerTxPriority;
 	type SignedRewardBase = SignedRewardBase;
-	type SignedDepositBase = SignedDepositBase;
+	type SignedDepositBase = Self;
+	type SignedFixedDepositBase = SignedFixedDepositBase;
+	type SignedDepositBaseIncreaseFactor = SignedDepositBaseIncreaseFactor;
 	type SignedDepositByte = ();
 	type SignedDepositWeight = ();
 	type SignedMaxWeight = SignedMaxWeight;
@@ -415,6 +421,18 @@ impl crate::Config for Runtime {
 	type Solver = SequentialPhragmen<AccountId, SolutionAccuracyOf<Runtime>, Balancing>;
 }
 
+impl Convert<usize, BalanceOf<Runtime>> for Runtime {
+	/// returns the geometric increase deposit fee if `EnableVariableDepositBase` is set, otherwise
+	/// the fee is `SignedFixedDepositBase`.
+	fn convert(queue_len: usize) -> Balance {
+		if !EnableVariableDepositBase::get() {
+			SignedFixedDepositBase::get()
+		} else {
+			GeometricDepositBase::<Runtime>::convert(queue_len)
+		}
+	}
+}
+
 impl<LocalCall> frame_system::offchain::SendTransactionTypes<LocalCall> for Runtime
 where
 	RuntimeCall: From<LocalCall>,
@@ -561,8 +579,14 @@ impl ExtBuilder {
 		<SignedMaxSubmissions>::set(count);
 		self
 	}
+	pub fn signed_base_deposit(self, base: u64, variable: bool, increase: Percent) -> Self {
+		<EnableVariableDepositBase>::set(variable);
+		<SignedFixedDepositBase>::set(base);
+		<SignedDepositBaseIncreaseFactor>::set(increase);
+		self
+	}
 	pub fn signed_deposit(self, base: u64, byte: u64, weight: u64) -> Self {
-		<SignedDepositBase>::set(base);
+		<SignedFixedDepositBase>::set(base);
 		<SignedDepositByte>::set(byte);
 		<SignedDepositWeight>::set(weight);
 		self

frame/election-provider-multi-phase/src/signed.rs

@@ -17,6 +17,8 @@
 
 //! The signed phase implementation.
 
+use core::marker::PhantomData;
+
 use crate::{
 	unsigned::MinerConfig, Config, ElectionCompute, Pallet, QueuedSolution, RawSolution,
 	ReadySolution, SignedSubmissionIndices, SignedSubmissionNextIndex, SignedSubmissionsMap,
@@ -31,8 +33,8 @@ use sp_arithmetic::traits::SaturatedConversion;
 use sp_core::bounded::BoundedVec;
 use sp_npos_elections::ElectionScore;
 use sp_runtime::{
-	traits::{Saturating, Zero},
-	RuntimeDebug,
+	traits::{Convert, Saturating, Zero},
+	FixedPointNumber, FixedU128, Percent, RuntimeDebug,
 };
 use sp_std::{
 	cmp::Ordering,
@@ -349,6 +351,31 @@ impl<T: Config> SignedSubmissions<T> {
 	}
 }
 
+/// Type that can be used to calculate the deposit base for signed submissions.
+///
+/// The deposit base is calculated as a geometric progression based on the number of signed
+/// submissions in the queue. The size of the queue represents the progression term.
+pub struct GeometricDepositBase<T> {
+	_marker: PhantomData<T>,
+}
+
+impl<T: Config> Convert<usize, BalanceOf<T>> for GeometricDepositBase<T> {
+	// Calculates the base deposit as a geometric progression based on the number of signed
+	// su Calculates.
+	//
+	// The nth term is obtained by calculating `base * (1 + increase_factor)^nth`. Example: factor
+	// 5, with initial deposit of 1000 and 10% of increase factor is 1000 * (1 + 0.1)^5.
+	fn convert(queue_len: usize) -> BalanceOf<T> {
+		let increase_factor: FixedU128 =
+			<Percent as Into<FixedU128>>::into(T::SignedDepositBaseIncreaseFactor::get()) +
+				sp_runtime::traits::One::one();
+
+		increase_factor
+			.saturating_pow(queue_len)
+			.saturating_mul_int(T::SignedFixedDepositBase::get())
+	}
+}
+
 impl<T: Config> Pallet<T> {
 	/// `Self` accessor for `SignedSubmission<T>`.
 	pub fn signed_submissions() -> SignedSubmissions<T> {
@@ -521,14 +548,14 @@ impl<T: Config> Pallet<T> {
 		size: SolutionOrSnapshotSize,
 	) -> BalanceOf<T> {
 		let encoded_len: u32 = raw_solution.encoded_size().saturated_into();
-		let encoded_len: BalanceOf<T> = encoded_len.into();
+		let encoded_len_balance: BalanceOf<T> = encoded_len.into();
 		let feasibility_weight = Self::solution_weight_of(raw_solution, size);
 
-		let len_deposit = T::SignedDepositByte::get().saturating_mul(encoded_len);
+		let len_deposit = T::SignedDepositByte::get().saturating_mul(encoded_len_balance);
 		let weight_deposit = T::SignedDepositWeight::get()
 			.saturating_mul(feasibility_weight.ref_time().saturated_into());
 
-		T::SignedDepositBase::get()
+		T::SignedDepositBase::convert(Self::signed_submissions().len())
 			.saturating_add(len_deposit)
 			.saturating_add(weight_deposit)
 	}
@@ -539,6 +566,7 @@ mod tests {
 	use super::*;
 	use crate::{mock::*, ElectionCompute, ElectionError, Error, Event, Perbill, Phase};
 	use frame_support::{assert_noop, assert_ok, assert_storage_noop};
+	use sp_runtime::Percent;
 
 	#[test]
 	fn cannot_submit_too_early() {
@@ -775,6 +803,56 @@ mod tests {
 		})
 	}
 
+	#[test]
+	fn geometric_deposit_queue_size_works() {
+		let constant = vec![1000; 10];
+		// geometric progression with 10% increase in each iteration for 10 terms.
+		let progression_10 = vec![1000, 1100, 1210, 1331, 1464, 1610, 1771, 1948, 2143, 2357];
+		let progression_40 = vec![1000, 1400, 1960, 2744, 3841, 5378, 7529, 10541, 14757, 20661];
+
+		let check_progressive_base_fee = |expected: &Vec<u64>| {
+			for s in 0..SignedMaxSubmissions::get() {
+				let account = 99 + s as u64;
+				Balances::make_free_balance_be(&account, 10000000);
+				let mut solution = raw_solution();
+				solution.score.minimal_stake -= s as u128;
+
+				assert_ok!(MultiPhase::submit(RuntimeOrigin::signed(account), Box::new(solution)));
+				assert_eq!(balances(&account).1, expected[s as usize])
+			}
+		};
+
+		ExtBuilder::default()
+			.signed_max_submission(10)
+			.signed_base_deposit(1000, true, Percent::from_percent(0))
+			.build_and_execute(|| {
+				roll_to_signed();
+				assert!(MultiPhase::current_phase().is_signed());
+
+				check_progressive_base_fee(&constant);
+			});
+
+		ExtBuilder::default()
+			.signed_max_submission(10)
+			.signed_base_deposit(1000, true, Percent::from_percent(10))
+			.build_and_execute(|| {
+				roll_to_signed();
+				assert!(MultiPhase::current_phase().is_signed());
+
+				check_progressive_base_fee(&progression_10);
+			});
+
+		ExtBuilder::default()
+			.signed_max_submission(10)
+			.signed_base_deposit(1000, true, Percent::from_percent(40))
+			.build_and_execute(|| {
+				roll_to_signed();
+				assert!(MultiPhase::current_phase().is_signed());
+
+				check_progressive_base_fee(&progression_40);
+			});
+	}
+
 	#[test]
 	fn call_fee_refund_is_limited_by_signed_max_refunds() {
 		ExtBuilder::default().build_and_execute(|| {

frame/election-provider-multi-phase/test-staking-e2e/src/mock.rs

@@ -29,7 +29,7 @@ use sp_npos_elections::{ElectionScore, VoteWeight};
 use sp_runtime::{
 	testing,
 	traits::{IdentityLookup, Zero},
-	transaction_validity, PerU16, Perbill,
+	transaction_validity, PerU16, Perbill, Percent,
 };
 use sp_staking::{
 	offence::{DisableStrategy, OffenceDetails, OnOffenceHandler},
@@ -40,7 +40,8 @@ use std::collections::BTreeMap;
 
 use frame_election_provider_support::{onchain, ElectionDataProvider, SequentialPhragmen, Weight};
 use pallet_election_provider_multi_phase::{
-	unsigned::MinerConfig, ElectionCompute, QueuedSolution, SolutionAccuracyOf,
+	unsigned::MinerConfig, ElectionCompute, GeometricDepositBase, QueuedSolution,
+	SolutionAccuracyOf,
 };
 use pallet_staking::StakerStatus;
 
@@ -190,7 +191,9 @@ parameter_types! {
 	pub static TransactionPriority: transaction_validity::TransactionPriority = 1;
 	pub static MaxWinners: u32 = 100;
 	pub static MaxVotesPerVoter: u32 = 16;
-	pub static MaxNominations: u32 = 16;
+	pub static MaxNominations: u32  = 16;
+	pub static SignedFixedDepositBase: Balance = 1;
+	pub static SignedDepositBaseIncreaseFactor: Percent = Percent::from_percent(10);
 }
 
 impl pallet_election_provider_multi_phase::Config for Runtime {
@@ -206,7 +209,9 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type MinerConfig = Self;
 	type SignedMaxSubmissions = ConstU32<10>;
 	type SignedRewardBase = ();
-	type SignedDepositBase = ();
+	type SignedDepositBase = GeometricDepositBase<Runtime>;
+	type SignedFixedDepositBase = SignedFixedDepositBase;
+	type SignedDepositBaseIncreaseFactor = SignedDepositBaseIncreaseFactor;
 	type SignedDepositByte = ();
 	type SignedMaxRefunds = ConstU32<3>;
 	type SignedDepositWeight = ();

frame/staking/src/lib.rs

@@ -159,7 +159,7 @@
 //! ```
 //! use pallet_staking::{self as staking};
 //!
-//! #[frame_support::pallet]
+//! #[frame_support::pallet(dev_mode)]
 //! pub mod pallet {
 //! 	use super::*;
 //! 	use frame_support::pallet_prelude::*;