Companion for Decouple Staking and Election - Part 3: Signed Phase (#2793)

* Companion for Decouple Staking and Election - Part 3: Signed Phase

https://github.com/paritytech/substrate/pull/7910

* remove some config types

* allow up to 5 signed submissions on polkadot and kusama

* signed phase is equal induration to unsigned phase

* use chain defaults for base and per-byte deposits; >= 16 SignedMaxSubmissions

* use a small but non-trivial solution reward

* reduce signed deposit per byte fee

* reduce signed reward, adjust polkadot expected soln size

* copy submit benchmark from substrate

* demo calculating an appropriate fee for the signed reward

Unfortunately, this doesn't work: it needs to be a constant function,
and AFAIK there's no way to make a trait method constant.

* SignedRewardBase is 1.5x the fee to submit a signed solution

* all chains use deposit byte of base per 50k

* update Substrate

* cargo update -p pallet-election-provider-multi-phase

Co-authored-by: parity-processbot <>

polkadot/runtime/common/Cargo.toml

@@ -35,7 +35,7 @@ pallet-vesting = { git = "https://github.com/paritytech/substrate", branch = "ma
 pallet-offences = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 pallet-transaction-payment = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 pallet-treasury = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
-
+pallet-election-provider-multi-phase = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 pallet-beefy = { git = "https://github.com/paritytech/grandpa-bridge-gadget", branch = "master", default-features = false }
 pallet-mmr = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 
@@ -91,6 +91,7 @@ std = [
 	"pallet-vesting/std",
 	"pallet-transaction-payment/std",
 	"pallet-treasury/std",
+	"pallet-election-provider-multi-phase/std",
 	"slot-range-helper/std",
 	"sp-runtime/std",
 	"sp-session/std",

polkadot/runtime/common/src/elections.rs

@@ -0,0 +1,61 @@
+// Copyright 2021 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Code for elections.
+
+use frame_support::{
+	parameter_types,
+	traits::Get,
+	weights::{DispatchClass, Weight, WeightToFeePolynomial},
+};
+use sp_runtime::Perbill;
+use super::{BlockExecutionWeight, BlockLength, BlockWeights};
+
+parameter_types! {
+	/// A limit for off-chain phragmen unsigned solution submission.
+	///
+	/// We want to keep it as high as possible, but can't risk having it reject,
+	/// so we always subtract the base block execution weight.
+	pub OffchainSolutionWeightLimit: Weight = BlockWeights::get()
+		.get(DispatchClass::Normal)
+		.max_extrinsic
+		.expect("Normal extrinsics have weight limit configured by default; qed")
+		.saturating_sub(BlockExecutionWeight::get());
+
+	/// A limit for off-chain phragmen unsigned solution length.
+	///
+	/// We allow up to 90% of the block's size to be consumed by the solution.
+	pub OffchainSolutionLengthLimit: u32 = Perbill::from_rational(90_u32, 100) *
+		*BlockLength::get()
+		.max
+		.get(DispatchClass::Normal);
+}
+
+/// Compute the expected fee for submitting an election solution.
+///
+/// This is `multiplier` multiplied by the fee for the expected submission weight according to the
+/// weight info.
+///
+/// Assumes that the signed submission queue is full.
+pub fn fee_for_submit_call<T, WeightToFee, WeightInfo>(multiplier: Perbill) -> WeightToFee::Balance
+where
+	T: pallet_election_provider_multi_phase::Config,
+	WeightToFee: WeightToFeePolynomial,
+	WeightInfo: pallet_election_provider_multi_phase::WeightInfo,
+{
+	let expected_weight = WeightInfo::submit(T::SignedMaxSubmissions::get());
+	multiplier * WeightToFee::calc(&expected_weight)
+}

polkadot/runtime/common/src/lib.rs

@@ -1,4 +1,4 @@
-// Copyright 2019-2020 Parity Technologies (UK) Ltd.
+// Copyright 2019-2021 Parity Technologies (UK) Ltd.
 // This file is part of Polkadot.
 
 // Polkadot is free software: you can redistribute it and/or modify
@@ -30,6 +30,7 @@ pub mod paras_registrar;
 pub mod slot_range;
 pub mod traits;
 pub mod xcm_sender;
+pub mod elections;
 
 #[cfg(test)]
 mod mock;
@@ -54,6 +55,7 @@ pub use pallet_staking::StakerStatus;
 pub use sp_runtime::BuildStorage;
 pub use pallet_timestamp::Call as TimestampCall;
 pub use pallet_balances::Call as BalancesCall;
+pub use elections::{OffchainSolutionLengthLimit, OffchainSolutionWeightLimit};
 
 /// Implementations of some helper traits passed into runtime modules as associated types.
 pub use impls::ToAuthor;
@@ -108,26 +110,6 @@ parameter_types! {
 		.build_or_panic();
 }
 
-parameter_types! {
-	/// A limit for off-chain phragmen unsigned solution submission.
-	///
-	/// We want to keep it as high as possible, but can't risk having it reject,
-	/// so we always subtract the base block execution weight.
-	pub OffchainSolutionWeightLimit: Weight = BlockWeights::get()
-		.get(DispatchClass::Normal)
-		.max_extrinsic
-		.expect("Normal extrinsics have weight limit configured by default; qed")
-		.saturating_sub(BlockExecutionWeight::get());
-
-	/// A limit for off-chain phragmen unsigned solution length.
-	///
-	/// We allow up to 90% of the block's size to be consumed by the solution.
-	pub OffchainSolutionLengthLimit: u32 = Perbill::from_rational(90_u32, 100) *
-		*BlockLength::get()
-		.max
-		.get(DispatchClass::Normal);
-}
-
 /// Parameterized slow adjusting fee updated based on
 /// https://w3f-research.readthedocs.io/en/latest/polkadot/Token%20Economics.html#-2.-slow-adjusting-mechanism
 pub type SlowAdjustingFeeUpdate<R> = TargetedFeeAdjustment<

polkadot/runtime/kusama/src/lib.rs

@@ -34,7 +34,8 @@ use primitives::v1::{
 use runtime_common::{
 	claims, paras_registrar, xcm_sender, slots, auctions, crowdloan,
 	SlowAdjustingFeeUpdate, CurrencyToVote, impls::DealWithFees,
-	BlockHashCount, RocksDbWeight, BlockWeights, BlockLength, OffchainSolutionWeightLimit, OffchainSolutionLengthLimit,
+	BlockHashCount, RocksDbWeight, BlockWeights, BlockLength,
+	OffchainSolutionWeightLimit, OffchainSolutionLengthLimit, elections::fee_for_submit_call,
 	ToAuthor,
 };
 
@@ -348,11 +349,24 @@ impl pallet_session::historical::Config for Runtime {
 }
 
 parameter_types! {
-	// no signed phase for now, just unsigned.
-	pub const SignedPhase: u32 = 0;
+	// phase durations. 1/4 of the last session for each.
+	pub const SignedPhase: u32 = EPOCH_DURATION_IN_SLOTS / 4;
 	pub const UnsignedPhase: u32 = EPOCH_DURATION_IN_SLOTS / 4;
 
-	// fallback: run election on-chain.
+	// signed config
+	pub const SignedMaxSubmissions: u32 = 16;
+	pub const SignedDepositBase: Balance = deposit(1, 0);
+	// A typical solution occupies within an order of magnitude of 50kb.
+	// This formula is currently adjusted such that a typical solution will spend an amount equal
+	// to the base deposit for every 50 kb.
+	pub const SignedDepositByte: Balance = deposit(1, 0) / (50 * 1024);
+	pub SignedRewardBase: Balance = fee_for_submit_call::<
+		Runtime,
+		crate::constants::fee::WeightToFee,
+		crate::weights::pallet_election_provider_multi_phase::WeightInfo<Runtime>,
+	>(Perbill::from_perthousand(1500));
+
+	// fallback: emergency phase.
 	pub const Fallback: pallet_election_provider_multi_phase::FallbackStrategy =
 		pallet_election_provider_multi_phase::FallbackStrategy::Nothing;
 	pub SolutionImprovementThreshold: Perbill = Perbill::from_rational(5u32, 10_000);
@@ -375,6 +389,14 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type Event = Event;
 	type Currency = Balances;
 	type UnsignedPhase = UnsignedPhase;
+	type SignedMaxSubmissions = SignedMaxSubmissions;
+	type SignedRewardBase = SignedRewardBase;
+	type SignedDepositBase = SignedDepositBase;
+	type SignedDepositByte = SignedDepositByte;
+	type SignedDepositWeight = ();
+	type SignedMaxWeight = Self::MinerMaxWeight;
+	type SlashHandler = (); // burn slashes
+	type RewardHandler = (); // nothing to do upon rewards
 	type SignedPhase = SignedPhase;
 	type SolutionImprovementThreshold = SolutionImprovementThreshold;
 	type MinerMaxIterations = MinerMaxIterations;

polkadot/runtime/kusama/src/weights/pallet_election_provider_multi_phase.rs

@@ -67,6 +67,13 @@ impl<T: frame_system::Config> pallet_election_provider_multi_phase::WeightInfo f
 			.saturating_add(T::DbWeight::get().reads(2 as Weight))
 			.saturating_add(T::DbWeight::get().writes(6 as Weight))
 	}
+	fn submit(c: u32, ) -> Weight {
+		(84_430_000 as Weight)
+			// Standard Error: 146_000
+			.saturating_add((2_758_000 as Weight).saturating_mul(c as Weight))
+			.saturating_add(T::DbWeight::get().reads(3 as Weight))
+			.saturating_add(T::DbWeight::get().writes(1 as Weight))
+	}
 	fn submit_unsigned(v: u32, t: u32, a: u32, d: u32, ) -> Weight {
 		(0 as Weight)
 			// Standard Error: 13_000
@@ -92,4 +99,14 @@ impl<T: frame_system::Config> pallet_election_provider_multi_phase::WeightInfo f
 			.saturating_add((4_469_000 as Weight).saturating_mul(d as Weight))
 			.saturating_add(T::DbWeight::get().reads(4 as Weight))
 	}
+	fn finalize_signed_phase_accept_solution() -> Weight {
+		(47_783_000 as Weight)
+			.saturating_add(T::DbWeight::get().reads(1 as Weight))
+			.saturating_add(T::DbWeight::get().writes(2 as Weight))
+	}
+	fn finalize_signed_phase_reject_solution() -> Weight {
+		(21_277_000 as Weight)
+			.saturating_add(T::DbWeight::get().reads(1 as Weight))
+			.saturating_add(T::DbWeight::get().writes(1 as Weight))
+	}
 }

polkadot/runtime/polkadot/src/lib.rs

@@ -26,6 +26,7 @@ use runtime_common::{
 	impls::DealWithFees,
 	BlockHashCount, RocksDbWeight, BlockWeights, BlockLength,
 	OffchainSolutionWeightLimit, OffchainSolutionLengthLimit,
+	elections::fee_for_submit_call,
 	ParachainSessionKeyPlaceholder, AssignmentSessionKeyPlaceholder,
 };
 
@@ -328,11 +329,24 @@ impl pallet_session::historical::Config for Runtime {
 }
 
 parameter_types! {
-	// no signed phase for now, just unsigned.
-	pub const SignedPhase: u32 = 0;
+	// phase durations. 1/4 of the last session for each.
+	pub const SignedPhase: u32 = EPOCH_DURATION_IN_SLOTS / 4;
 	pub const UnsignedPhase: u32 = EPOCH_DURATION_IN_SLOTS / 4;
 
-	// fallback: run election on-chain.
+	// signed config
+	pub const SignedMaxSubmissions: u32 = 16;
+	pub const SignedDepositBase: Balance = deposit(1, 0);
+	// A typical solution occupies within an order of magnitude of 50kb.
+	// This formula is currently adjusted such that a typical solution will spend an amount equal
+	// to the base deposit for every 50 kb.
+	pub const SignedDepositByte: Balance = deposit(1, 0) / (50 * 1024);
+	pub SignedRewardBase: Balance = fee_for_submit_call::<
+		Runtime,
+		crate::constants::fee::WeightToFee,
+		crate::weights::pallet_election_provider_multi_phase::WeightInfo<Runtime>,
+	>(Perbill::from_perthousand(1500));
+
+	// fallback: emergency phase.
 	pub const Fallback: pallet_election_provider_multi_phase::FallbackStrategy =
 		pallet_election_provider_multi_phase::FallbackStrategy::Nothing;
 	pub SolutionImprovementThreshold: Perbill = Perbill::from_rational(5u32, 10_000);
@@ -356,6 +370,14 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type Currency = Balances;
 	type SignedPhase = SignedPhase;
 	type UnsignedPhase = UnsignedPhase;
+	type SignedMaxSubmissions = SignedMaxSubmissions;
+	type SignedRewardBase = SignedRewardBase;
+	type SignedDepositBase = SignedDepositBase;
+	type SignedDepositByte = SignedDepositByte;
+	type SignedDepositWeight = ();
+	type SignedMaxWeight = Self::MinerMaxWeight;
+	type SlashHandler = (); // burn slashes
+	type RewardHandler = (); // nothing to do upon rewards
 	type SolutionImprovementThreshold = SolutionImprovementThreshold;
 	type MinerMaxIterations = MinerMaxIterations;
 	type MinerMaxWeight = OffchainSolutionWeightLimit; // For now use the one from staking.

polkadot/runtime/polkadot/src/weights/pallet_election_provider_multi_phase.rs

@@ -92,4 +92,21 @@ impl<T: frame_system::Config> pallet_election_provider_multi_phase::WeightInfo f
 			.saturating_add((3_606_000 as Weight).saturating_mul(d as Weight))
 			.saturating_add(T::DbWeight::get().reads(4 as Weight))
 	}
+	fn finalize_signed_phase_accept_solution() -> Weight {
+		(47_783_000 as Weight)
+			.saturating_add(T::DbWeight::get().reads(1 as Weight))
+			.saturating_add(T::DbWeight::get().writes(2 as Weight))
+	}
+	fn finalize_signed_phase_reject_solution() -> Weight {
+		(21_277_000 as Weight)
+			.saturating_add(T::DbWeight::get().reads(1 as Weight))
+			.saturating_add(T::DbWeight::get().writes(1 as Weight))
+	}
+	fn submit(c: u32) -> Weight {
+		(78_972_000 as Weight)
+			// Standard Error: 16_000
+			.saturating_add((308_000 as Weight).saturating_mul(c as Weight))
+			.saturating_add(T::DbWeight::get().reads(4 as Weight))
+			.saturating_add(T::DbWeight::get().writes(3 as Weight))
+	}
 }

polkadot/runtime/westend/src/lib.rs

@@ -36,6 +36,7 @@ use runtime_common::{
 	impls::ToAuthor,
 	BlockHashCount, BlockWeights, BlockLength, RocksDbWeight,
 	OffchainSolutionWeightLimit, OffchainSolutionLengthLimit,
+	elections::fee_for_submit_call,
 };
 
 use runtime_parachains::origin as parachains_origin;
@@ -333,11 +334,24 @@ impl pallet_session::historical::Config for Runtime {
 }
 
 parameter_types! {
-	// no signed phase for now, just unsigned.
-	pub const SignedPhase: u32 = 0;
+	// phase durations. 1/4 of the last session for each.
+	pub const SignedPhase: u32 = EPOCH_DURATION_IN_SLOTS / 4;
 	pub const UnsignedPhase: u32 = EPOCH_DURATION_IN_SLOTS / 4;
 
-	// fallback: run election on-chain.
+	// signed config
+	pub const SignedMaxSubmissions: u32 = 128;
+	pub const SignedDepositBase: Balance = deposit(1, 0);
+	// A typical solution occupies within an order of magnitude of 50kb.
+	// This formula is currently adjusted such that a typical solution will spend an amount equal
+	// to the base deposit for every 50 kb.
+	pub const SignedDepositByte: Balance = deposit(1, 0) / (50 * 1024);
+	pub SignedRewardBase: Balance = fee_for_submit_call::<
+		Runtime,
+		crate::constants::fee::WeightToFee,
+		crate::weights::pallet_election_provider_multi_phase::WeightInfo<Runtime>,
+	>(Perbill::from_perthousand(1500));
+
+	// fallback: emergency phase.
 	pub const Fallback: pallet_election_provider_multi_phase::FallbackStrategy =
 		pallet_election_provider_multi_phase::FallbackStrategy::Nothing;
 
@@ -362,6 +376,14 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type Currency = Balances;
 	type SignedPhase = SignedPhase;
 	type UnsignedPhase = UnsignedPhase;
+	type SignedMaxSubmissions = SignedMaxSubmissions;
+	type SignedRewardBase = SignedRewardBase;
+	type SignedDepositBase = SignedDepositBase;
+	type SignedDepositByte = SignedDepositByte;
+	type SignedDepositWeight = ();
+	type SignedMaxWeight = Self::MinerMaxWeight;
+	type SlashHandler = (); // burn slashes
+	type RewardHandler = (); // nothing to do upon rewards
 	type SolutionImprovementThreshold = SolutionImprovementThreshold;
 	type MinerMaxIterations = MinerMaxIterations;
 	type MinerMaxWeight = OffchainSolutionWeightLimit; // For now use the one from staking.

polkadot/runtime/westend/src/weights/pallet_election_provider_multi_phase.rs

@@ -92,4 +92,21 @@ impl<T: frame_system::Config> pallet_election_provider_multi_phase::WeightInfo f
 			.saturating_add((3_731_000 as Weight).saturating_mul(d as Weight))
 			.saturating_add(T::DbWeight::get().reads(4 as Weight))
 	}
+	fn finalize_signed_phase_accept_solution() -> Weight {
+		(47_783_000 as Weight)
+			.saturating_add(T::DbWeight::get().reads(1 as Weight))
+			.saturating_add(T::DbWeight::get().writes(2 as Weight))
+	}
+	fn finalize_signed_phase_reject_solution() -> Weight {
+		(21_277_000 as Weight)
+			.saturating_add(T::DbWeight::get().reads(1 as Weight))
+			.saturating_add(T::DbWeight::get().writes(1 as Weight))
+	}
+	fn submit(c: u32) -> Weight {
+		(78_972_000 as Weight)
+			// Standard Error: 16_000
+			.saturating_add((308_000 as Weight).saturating_mul(c as Weight))
+			.saturating_add(T::DbWeight::get().reads(4 as Weight))
+			.saturating_add(T::DbWeight::get().writes(3 as Weight))
+	}
 }