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/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)
+}