Update polkadot inflation to take into account auctions (#5872)

* Update polkadot inflation to take into account auctions

* a possible solution -- but needs a rather untrivial data seeding

* some additional comments

* Use LOWEST_PUBLIC_ID as a guide to filter out system/common good para ids

* Fixes

* move tests

* fix

Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

runtime/common/Cargo.toml

@@ -31,6 +31,7 @@ pallet-balances = { git = "https://github.com/paritytech/substrate", branch = "m
 pallet-session = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 frame-support = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 pallet-staking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+pallet-staking-reward-fn = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 frame-system = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 pallet-timestamp = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 pallet-vesting = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
@@ -84,6 +85,7 @@ std = [
 	"pallet-beefy-mmr/std",
 	"pallet-session/std",
 	"pallet-staking/std",
+	"pallet-staking-reward-fn/std",
 	"pallet-timestamp/std",
 	"pallet-vesting/std",
 	"pallet-transaction-payment/std",

runtime/common/src/impls.rs

@@ -18,6 +18,8 @@
 
 use crate::NegativeImbalance;
 use frame_support::traits::{Currency, Imbalance, OnUnbalanced};
+use primitives::v2::Balance;
+use sp_runtime::Perquintill;
 
 /// Logic for the author to get a portion of fees.
 pub struct ToAuthor<R>(sp_std::marker::PhantomData<R>);
@@ -57,6 +59,45 @@ where
 	}
 }
 
+pub fn era_payout(
+	total_staked: Balance,
+	non_gilt_issuance: Balance,
+	max_annual_inflation: Perquintill,
+	period_fraction: Perquintill,
+	auctioned_slots: u64,
+) -> (Balance, Balance) {
+	use pallet_staking_reward_fn::compute_inflation;
+	use sp_runtime::traits::Saturating;
+
+	let min_annual_inflation = Perquintill::from_rational(25u64, 1000u64);
+	let delta_annual_inflation = max_annual_inflation.saturating_sub(min_annual_inflation);
+
+	// 30% reserved for up to 60 slots.
+	let auction_proportion = Perquintill::from_rational(auctioned_slots.min(60), 200u64);
+
+	// Therefore the ideal amount at stake (as a percentage of total issuance) is 75% less the
+	// amount that we expect to be taken up with auctions.
+	let ideal_stake = Perquintill::from_percent(75).saturating_sub(auction_proportion);
+
+	let stake = Perquintill::from_rational(total_staked, non_gilt_issuance);
+	let falloff = Perquintill::from_percent(5);
+	let adjustment = compute_inflation(stake, ideal_stake, falloff);
+	let staking_inflation =
+		min_annual_inflation.saturating_add(delta_annual_inflation * adjustment);
+
+	let max_payout = period_fraction * max_annual_inflation * non_gilt_issuance;
+	let staking_payout = (period_fraction * staking_inflation) * non_gilt_issuance;
+	let rest = max_payout.saturating_sub(staking_payout);
+
+	let other_issuance = non_gilt_issuance.saturating_sub(total_staked);
+	if total_staked > other_issuance {
+		let _cap_rest = Perquintill::from_rational(other_issuance, total_staked) * staking_payout;
+		// We don't do anything with this, but if we wanted to, we could introduce a cap on the
+		// treasury amount with: `rest = rest.min(cap_rest);`
+	}
+	(staking_payout, rest)
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;
@@ -209,4 +250,44 @@ mod tests {
 			assert_eq!(Balances::free_balance(Treasury::account_id()), 8);
 		});
 	}
+
+	#[test]
+	fn compute_inflation_should_give_sensible_results() {
+		assert_eq!(
+			pallet_staking_reward_fn::compute_inflation(
+				Perquintill::from_percent(75),
+				Perquintill::from_percent(75),
+				Perquintill::from_percent(5),
+			),
+			Perquintill::one()
+		);
+		assert_eq!(
+			pallet_staking_reward_fn::compute_inflation(
+				Perquintill::from_percent(50),
+				Perquintill::from_percent(75),
+				Perquintill::from_percent(5),
+			),
+			Perquintill::from_rational(2u64, 3u64)
+		);
+		assert_eq!(
+			pallet_staking_reward_fn::compute_inflation(
+				Perquintill::from_percent(80),
+				Perquintill::from_percent(75),
+				Perquintill::from_percent(5),
+			),
+			Perquintill::from_rational(1u64, 2u64)
+		);
+	}
+
+	#[test]
+	fn era_payout_should_give_sensible_results() {
+		assert_eq!(
+			era_payout(75, 100, Perquintill::from_percent(10), Perquintill::one(), 0,),
+			(10, 0)
+		);
+		assert_eq!(
+			era_payout(80, 100, Perquintill::from_percent(10), Perquintill::one(), 0,),
+			(6, 4)
+		);
+	}
 }

runtime/kusama/Cargo.toml

@@ -72,7 +72,6 @@ pallet-session = { git = "https://github.com/paritytech/substrate", branch = "ma
 pallet-society = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 frame-support = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 pallet-staking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
-pallet-staking-reward-fn = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 frame-system = {git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 frame-system-rpc-runtime-api = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 pallet-timestamp = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
@@ -170,7 +169,6 @@ std = [
 	"pallet-session/std",
 	"pallet-society/std",
 	"pallet-staking/std",
-	"pallet-staking-reward-fn/std",
 	"pallet-timestamp/std",
 	"pallet-tips/std",
 	"pallet-treasury/std",

runtime/kusama/src/lib.rs

@@ -26,6 +26,7 @@ use primitives::v2::{
 	CoreState, GroupRotationInfo, Hash, Id as ParaId, InboundDownwardMessage, InboundHrmpMessage,
 	Moment, Nonce, OccupiedCoreAssumption, PersistedValidationData, ScrapedOnChainVotes,
 	SessionInfo, Signature, ValidationCode, ValidationCodeHash, ValidatorId, ValidatorIndex,
+	LOWEST_PUBLIC_ID,
 };
 use runtime_common::{
 	auctions, claims, crowdloan, impl_runtime_weights, impls::DealWithFees, paras_registrar,
@@ -504,59 +505,25 @@ impl pallet_bags_list::Config<VoterBagsListInstance> for Runtime {
 	type Score = sp_npos_elections::VoteWeight;
 }
 
-fn era_payout(
-	total_staked: Balance,
-	non_gilt_issuance: Balance,
-	max_annual_inflation: Perquintill,
-	period_fraction: Perquintill,
-	auctioned_slots: u64,
-) -> (Balance, Balance) {
-	use pallet_staking_reward_fn::compute_inflation;
-	use sp_arithmetic::traits::Saturating;
-
-	let min_annual_inflation = Perquintill::from_rational(25u64, 1000u64);
-	let delta_annual_inflation = max_annual_inflation.saturating_sub(min_annual_inflation);
-
-	// 30% reserved for up to 60 slots.
-	let auction_proportion = Perquintill::from_rational(auctioned_slots.min(60), 200u64);
-
-	// Therefore the ideal amount at stake (as a percentage of total issuance) is 75% less the amount that we expect
-	// to be taken up with auctions.
-	let ideal_stake = Perquintill::from_percent(75).saturating_sub(auction_proportion);
-
-	let stake = Perquintill::from_rational(total_staked, non_gilt_issuance);
-	let falloff = Perquintill::from_percent(5);
-	let adjustment = compute_inflation(stake, ideal_stake, falloff);
-	let staking_inflation =
-		min_annual_inflation.saturating_add(delta_annual_inflation * adjustment);
-
-	let max_payout = period_fraction * max_annual_inflation * non_gilt_issuance;
-	let staking_payout = (period_fraction * staking_inflation) * non_gilt_issuance;
-	let rest = max_payout.saturating_sub(staking_payout);
-
-	let other_issuance = non_gilt_issuance.saturating_sub(total_staked);
-	if total_staked > other_issuance {
-		let _cap_rest = Perquintill::from_rational(other_issuance, total_staked) * staking_payout;
-		// We don't do anything with this, but if we wanted to, we could introduce a cap on the treasury amount
-		// with: `rest = rest.min(cap_rest);`
-	}
-	(staking_payout, rest)
-}
-
 pub struct EraPayout;
 impl pallet_staking::EraPayout<Balance> for EraPayout {
 	fn era_payout(
 		total_staked: Balance,
 		_total_issuance: Balance,
 		era_duration_millis: u64,
 	) -> (Balance, Balance) {
-		// TODO: #3011 Update with proper auctioned slots tracking.
-		// This should be fine for the first year of parachains.
-		let auctioned_slots: u64 = auctions::Pallet::<Runtime>::auction_counter().into();
+		// all para-ids that are currently active.
+		let auctioned_slots = Paras::parachains()
+			.into_iter()
+			// all active para-ids that do not belong to a system or common good chain is the number
+			// of parachains that we should take into account for inflation.
+			.filter(|i| *i >= LOWEST_PUBLIC_ID)
+			.count() as u64;
+
 		const MAX_ANNUAL_INFLATION: Perquintill = Perquintill::from_percent(10);
 		const MILLISECONDS_PER_YEAR: u64 = 1000 * 3600 * 24 * 36525 / 100;
 
-		era_payout(
+		runtime_common::impls::era_payout(
 			total_staked,
 			Gilt::issuance().non_gilt,
 			MAX_ANNUAL_INFLATION,

runtime/kusama/src/tests.rs

@@ -137,40 +137,6 @@ fn nominator_limit() {
 	println!("can support {} nominators to yield a weight of {}", active, weight_with(active));
 }
 
-#[test]
-fn compute_inflation_should_give_sensible_results() {
-	assert_eq!(
-		pallet_staking_reward_fn::compute_inflation(
-			Perquintill::from_percent(75),
-			Perquintill::from_percent(75),
-			Perquintill::from_percent(5),
-		),
-		Perquintill::one()
-	);
-	assert_eq!(
-		pallet_staking_reward_fn::compute_inflation(
-			Perquintill::from_percent(50),
-			Perquintill::from_percent(75),
-			Perquintill::from_percent(5),
-		),
-		Perquintill::from_rational(2u64, 3u64)
-	);
-	assert_eq!(
-		pallet_staking_reward_fn::compute_inflation(
-			Perquintill::from_percent(80),
-			Perquintill::from_percent(75),
-			Perquintill::from_percent(5),
-		),
-		Perquintill::from_rational(1u64, 2u64)
-	);
-}
-
-#[test]
-fn era_payout_should_give_sensible_results() {
-	assert_eq!(era_payout(75, 100, Perquintill::from_percent(10), Perquintill::one(), 0,), (10, 0));
-	assert_eq!(era_payout(80, 100, Perquintill::from_percent(10), Perquintill::one(), 0,), (6, 4));
-}
-
 #[test]
 fn call_size() {
 	RuntimeCall::assert_size_under(230);

runtime/polkadot/src/lib.rs

@@ -58,6 +58,7 @@ use primitives::v2::{
 	CoreState, GroupRotationInfo, Hash, Id as ParaId, InboundDownwardMessage, InboundHrmpMessage,
 	Moment, Nonce, OccupiedCoreAssumption, PersistedValidationData, ScrapedOnChainVotes,
 	SessionInfo, Signature, ValidationCode, ValidationCodeHash, ValidatorId, ValidatorIndex,
+	LOWEST_PUBLIC_ID,
 };
 use sp_core::OpaqueMetadata;
 use sp_mmr_primitives as mmr;
@@ -536,6 +537,35 @@ type SlashCancelOrigin = EitherOfDiverse<
 	pallet_collective::EnsureProportionAtLeast<AccountId, CouncilCollective, 3, 4>,
 >;
 
+pub struct EraPayout;
+impl pallet_staking::EraPayout<Balance> for EraPayout {
+	fn era_payout(
+		total_staked: Balance,
+		total_issuance: Balance,
+		era_duration_millis: u64,
+	) -> (Balance, Balance) {
+		// all para-ids that are not active.
+		let auctioned_slots = Paras::parachains()
+			.into_iter()
+			// all active para-ids that do not belong to a system or common good chain is the number
+			// of parachains that we should take into account for inflation.
+			.filter(|i| *i >= LOWEST_PUBLIC_ID)
+			.count() as u64;
+
+		const MAX_ANNUAL_INFLATION: Perquintill = Perquintill::from_percent(10);
+		const MILLISECONDS_PER_YEAR: u64 = 1000 * 3600 * 24 * 36525 / 100;
+
+		runtime_common::impls::era_payout(
+			total_staked,
+			// Polkadot has no notion of gilts, the entire issuance is non-guilt.
+			total_issuance,
+			MAX_ANNUAL_INFLATION,
+			Perquintill::from_rational(era_duration_millis, MILLISECONDS_PER_YEAR),
+			auctioned_slots,
+		)
+	}
+}
+
 impl pallet_staking::Config for Runtime {
 	type MaxNominations = MaxNominations;
 	type Currency = Balances;
@@ -552,7 +582,7 @@ impl pallet_staking::Config for Runtime {
 	// A super-majority of the council can cancel the slash.
 	type SlashCancelOrigin = SlashCancelOrigin;
 	type SessionInterface = Self;
-	type EraPayout = pallet_staking::ConvertCurve<RewardCurve>;
+	type EraPayout = EraPayout;
 	type MaxNominatorRewardedPerValidator = MaxNominatorRewardedPerValidator;
 	type OffendingValidatorsThreshold = OffendingValidatorsThreshold;
 	type NextNewSession = Session;