Use Vote Ancestries Directly in Weight Calculations (#862)

* Use more accurate weight calculation in declared weight

* Remove session length and validator set size config constants

* Remove config params from mock

* Allow specifying total number of votes-ancestries per justification

* Change limits used during benchmarking

* Regenerate weights

* Use simplified weight annotation

* Remove comment

* Address leftover TODO

* Prevent possible divide by zero errors

* Use correct argument order in weight declaration

bridges/modules/grandpa/src/benchmarking.rs

@@ -51,13 +51,23 @@ use bp_test_utils::{
 	TEST_GRANDPA_ROUND, TEST_GRANDPA_SET_ID,
 };
 use frame_benchmarking::{benchmarks_instance_pallet, whitelisted_caller};
-use frame_support::traits::Get;
 use frame_system::RawOrigin;
-use num_traits::cast::AsPrimitive;
 use sp_finality_grandpa::AuthorityId;
 use sp_runtime::traits::{One, Zero};
 use sp_std::{vec, vec::Vec};
 
+// The maximum number of vote ancestries to include in a justification.
+//
+// In practice this would be limited by the session length (number of blocks a single authority set
+// can produce) of a given chain.
+const MAX_VOTE_ANCESTRIES: u32 = 1000;
+
+// The maximum number of pre-commits to include in a justification. In practice this scales with the
+// number of validators.
+//
+// TODO [#846]: Right now this will break benchmarking if it is greater than `u8::MAX`
+const MAX_VALIDATOR_SET_SIZE: u32 = 255;
+
 benchmarks_instance_pallet! {
 	// This is the "gold standard" benchmark for this extrinsic, and it's what should be used to
 	// annotate the weight in the pallet.
@@ -65,8 +75,8 @@ benchmarks_instance_pallet! {
 	// The other benchmarks related to `submit_finality_proof` are looking at the effect of specific
 	// parameters and are there mostly for seeing how specific codepaths behave.
 	submit_finality_proof {
-		let s in 1..T::MaxBridgedSessionLength::get().as_() as u32;
-		let p in 1..T::MaxBridgedValidatorCount::get();
+		let v in 1..MAX_VOTE_ANCESTRIES;
+		let p in 1..MAX_VALIDATOR_SET_SIZE;
 
 		let caller: T::AccountId = whitelisted_caller();
 
@@ -90,8 +100,8 @@ benchmarks_instance_pallet! {
 			round: TEST_GRANDPA_ROUND,
 			set_id: TEST_GRANDPA_SET_ID,
 			authorities: accounts(p as u8).iter().map(|k| (*k, 1)).collect::<Vec<_>>(),
-			depth: s,
-			forks: p,
+			votes: v,
+			forks: 1,
 		};
 
 		let justification = make_justification_for_header(params);
@@ -108,7 +118,7 @@ benchmarks_instance_pallet! {
 	// What we want to check here is the effect of vote ancestries on justification verification
 	// do this by varying the number of headers between `finality_target` and `header_of_chain`.
 	submit_finality_proof_on_single_fork {
-		let s in 1..T::MaxBridgedSessionLength::get().as_() as u32;
+		let v in 1..MAX_VOTE_ANCESTRIES;
 
 		let caller: T::AccountId = whitelisted_caller();
 
@@ -127,7 +137,7 @@ benchmarks_instance_pallet! {
 			round: TEST_GRANDPA_ROUND,
 			set_id: TEST_GRANDPA_SET_ID,
 			authorities: test_keyring(),
-			depth: s,
+			votes: v,
 			forks: 1,
 		};
 
@@ -146,7 +156,7 @@ benchmarks_instance_pallet! {
 	// We do this by creating many forks, whose head will be used as a signed pre-commit in the
 	// final justification.
 	submit_finality_proof_on_many_forks {
-		let p in 1..T::MaxBridgedValidatorCount::get();
+		let p in 1..MAX_VALIDATOR_SET_SIZE;
 
 		let caller: T::AccountId = whitelisted_caller();
 
@@ -170,7 +180,7 @@ benchmarks_instance_pallet! {
 			round: TEST_GRANDPA_ROUND,
 			set_id: TEST_GRANDPA_SET_ID,
 			authorities: accounts(p as u8).iter().map(|k| (*k, 1)).collect::<Vec<_>>(),
-			depth: 2,
+			votes: p,
 			forks: p,
 		};
 

bridges/modules/grandpa/src/lib.rs

@@ -44,7 +44,6 @@ use codec::{Decode, Encode};
 use finality_grandpa::voter_set::VoterSet;
 use frame_support::ensure;
 use frame_system::{ensure_signed, RawOrigin};
-use num_traits::cast::AsPrimitive;
 #[cfg(feature = "std")]
 use serde::{Deserialize, Serialize};
 use sp_finality_grandpa::{ConsensusLog, GRANDPA_ENGINE_ID};
@@ -92,27 +91,6 @@ pub mod pallet {
 		#[pallet::constant]
 		type MaxRequests: Get<u32>;
 
-		/// The maximum length of a session on the bridged chain.
-		///
-		/// The pallet uses this to bound justification verification since justifications contain
-		/// ancestry proofs whose size is capped at `MaxBridgedSessionLength`.
-		#[pallet::constant]
-		type MaxBridgedSessionLength: Get<BridgedBlockNumber<Self, I>>;
-
-		/// The number of validators on the bridged chain.
-		///
-		/// The pallet uses this to bound justification verification since justifications may
-		/// contain up to `MaxBridgedValidatorCount` number of signed `pre-commit` messages which
-		/// need to be verified.
-		///
-		/// Note that `MaxBridgedValidatorCount` should *not* match the exact number of validators
-		/// on the bridged chain. Instead it should be a number which is greater than the actual
-		/// number of validators in order to provide some buffer room should the validator set
-		/// increase in size. If this number ends up being lower than the actual number of
-		/// validators on the bridged chain you risk stalling the bridge.
-		#[pallet::constant]
-		type MaxBridgedValidatorCount: Get<u32>;
-
 		/// Weights gathered through benchmarking.
 		type WeightInfo: WeightInfo;
 	}
@@ -141,8 +119,8 @@ pub mod pallet {
 		/// If successful in verification, it will write the target header to the underlying storage
 		/// pallet.
 		#[pallet::weight(T::WeightInfo::submit_finality_proof(
-			T::MaxBridgedSessionLength::get().as_() as u32,
-			T::MaxBridgedValidatorCount::get(),
+			justification.votes_ancestries.len() as u32,
+			justification.commit.precommits.len() as u32,
 		))]
 		pub fn submit_finality_proof(
 			origin: OriginFor<T>,
@@ -181,15 +159,7 @@ pub mod pallet {
 
 			log::info!(target: "runtime::bridge-grandpa", "Succesfully imported finalized header with hash {:?}!", hash);
 
-			// Note that the number of precommits is indicitive of the number of GRANDPA forks being
-			// voted on.
-			let precommits = justification.commit.precommits.len();
-
-			// This represents the average number of votes in a single fork since the weight formula
-			// uses that metric instead of the aggregated number of vote ancestries.
-			let votes = (justification.votes_ancestries.len() + precommits - 1) / precommits;
-
-			Ok(Some(T::WeightInfo::submit_finality_proof(votes as u32, precommits as u32)).into())
+			Ok(().into())
 		}
 
 		/// Bootstrap the bridge pallet with an initial header and authority set from which to sync.

bridges/modules/grandpa/src/mock.rs

@@ -87,8 +87,6 @@ parameter_types! {
 impl grandpa::Config for TestRuntime {
 	type BridgedChain = TestBridgedChain;
 	type MaxRequests = MaxRequests;
-	type MaxBridgedSessionLength = SessionLength;
-	type MaxBridgedValidatorCount = NumValidators;
 	type WeightInfo = ();
 }
 

bridges/modules/grandpa/src/weights.rs

@@ -1,4 +1,4 @@
-// Copyright 2021 Parity Technologies (UK) Ltd.
+// Copyright 2019-2021 Parity Technologies (UK) Ltd.
 // This file is part of Parity Bridges Common.
 
 // Parity Bridges Common is free software: you can redistribute it and/or modify
@@ -17,7 +17,7 @@
 //! Autogenerated weights for pallet_bridge_grandpa
 //!
 //! THIS FILE WAS AUTO-GENERATED USING THE SUBSTRATE BENCHMARK CLI VERSION 3.0.0
-//! DATE: 2021-03-26, STEPS: [50, ], REPEAT: 20
+//! DATE: 2021-04-02, STEPS: [50, ], REPEAT: 20
 //! LOW RANGE: [], HIGH RANGE: []
 //! EXECUTION: Some(Wasm), WASM-EXECUTION: Compiled
 //! CHAIN: Some("dev"), DB CACHE: 128
@@ -57,85 +57,74 @@ use sp_std::marker::PhantomData;
 
 /// Weight functions needed for pallet_bridge_grandpa.
 pub trait WeightInfo {
-	fn submit_finality_proof(s: u32, p: u32) -> Weight;
-	fn submit_finality_proof_on_single_fork(s: u32) -> Weight;
+	fn submit_finality_proof(v: u32, p: u32) -> Weight;
+	fn submit_finality_proof_on_single_fork(v: u32) -> Weight;
 	fn submit_finality_proof_on_many_forks(p: u32) -> Weight;
 	fn find_scheduled_change(n: u32) -> Weight;
 	fn read_write_authority_sets(n: u32) -> Weight;
-	fn write_authority_sets(n: u32) -> Weight;
 }
 
 /// Weights for pallet_bridge_grandpa using the Rialto node and recommended hardware.
 pub struct RialtoWeight<T>(PhantomData<T>);
 impl<T: frame_system::Config> WeightInfo for RialtoWeight<T> {
-	fn submit_finality_proof(s: u32, p: u32) -> Weight {
+	fn submit_finality_proof(v: u32, p: u32) -> Weight {
 		(0 as Weight)
-			.saturating_add((3_248_661_000 as Weight).saturating_mul(s as Weight))
-			.saturating_add((776_552_000 as Weight).saturating_mul(p as Weight))
+			.saturating_add((160_060_000 as Weight).saturating_mul(v as Weight))
+			.saturating_add((640_223_000 as Weight).saturating_mul(p as Weight))
 			.saturating_add(T::DbWeight::get().reads(5 as Weight))
 			.saturating_add(T::DbWeight::get().writes(3 as Weight))
 	}
-	fn submit_finality_proof_on_single_fork(s: u32) -> Weight {
-		(189_213_000 as Weight)
-			.saturating_add((12_937_000 as Weight).saturating_mul(s as Weight))
+	fn submit_finality_proof_on_single_fork(v: u32) -> Weight {
+		(189_597_000 as Weight)
+			.saturating_add((11_680_000 as Weight).saturating_mul(v as Weight))
 			.saturating_add(T::DbWeight::get().reads(5 as Weight))
 			.saturating_add(T::DbWeight::get().writes(3 as Weight))
 	}
 	fn submit_finality_proof_on_many_forks(p: u32) -> Weight {
 		(0 as Weight)
-			.saturating_add((138_751_000 as Weight).saturating_mul(p as Weight))
+			.saturating_add((130_061_000 as Weight).saturating_mul(p as Weight))
 			.saturating_add(T::DbWeight::get().reads(5 as Weight))
 			.saturating_add(T::DbWeight::get().writes(3 as Weight))
 	}
 	fn find_scheduled_change(n: u32) -> Weight {
-		(301_000 as Weight).saturating_add((10_000 as Weight).saturating_mul(n as Weight))
+		(502_000 as Weight).saturating_add((8_000 as Weight).saturating_mul(n as Weight))
 	}
 	fn read_write_authority_sets(n: u32) -> Weight {
-		(6_787_000 as Weight)
-			.saturating_add((247_000 as Weight).saturating_mul(n as Weight))
+		(7_677_000 as Weight)
+			.saturating_add((230_000 as Weight).saturating_mul(n as Weight))
 			.saturating_add(T::DbWeight::get().reads(1 as Weight))
 			.saturating_add(T::DbWeight::get().writes(1 as Weight))
 	}
-	fn write_authority_sets(n: u32) -> Weight {
-		(3_383_000 as Weight)
-			.saturating_add((99_000 as Weight).saturating_mul(n as Weight))
-			.saturating_add(T::DbWeight::get().writes(1 as Weight))
-	}
 }
 
 // For backwards compatibility and tests
 impl WeightInfo for () {
-	fn submit_finality_proof(s: u32, p: u32) -> Weight {
+	fn submit_finality_proof(v: u32, p: u32) -> Weight {
 		(0 as Weight)
-			.saturating_add((3_248_661_000 as Weight).saturating_mul(s as Weight))
-			.saturating_add((776_552_000 as Weight).saturating_mul(p as Weight))
+			.saturating_add((160_060_000 as Weight).saturating_mul(v as Weight))
+			.saturating_add((640_223_000 as Weight).saturating_mul(p as Weight))
 			.saturating_add(RocksDbWeight::get().reads(5 as Weight))
 			.saturating_add(RocksDbWeight::get().writes(3 as Weight))
 	}
-	fn submit_finality_proof_on_single_fork(s: u32) -> Weight {
-		(189_213_000 as Weight)
-			.saturating_add((12_937_000 as Weight).saturating_mul(s as Weight))
+	fn submit_finality_proof_on_single_fork(v: u32) -> Weight {
+		(189_597_000 as Weight)
+			.saturating_add((11_680_000 as Weight).saturating_mul(v as Weight))
 			.saturating_add(RocksDbWeight::get().reads(5 as Weight))
 			.saturating_add(RocksDbWeight::get().writes(3 as Weight))
 	}
 	fn submit_finality_proof_on_many_forks(p: u32) -> Weight {
 		(0 as Weight)
-			.saturating_add((138_751_000 as Weight).saturating_mul(p as Weight))
+			.saturating_add((130_061_000 as Weight).saturating_mul(p as Weight))
 			.saturating_add(RocksDbWeight::get().reads(5 as Weight))
 			.saturating_add(RocksDbWeight::get().writes(3 as Weight))
 	}
 	fn find_scheduled_change(n: u32) -> Weight {
-		(301_000 as Weight).saturating_add((10_000 as Weight).saturating_mul(n as Weight))
+		(502_000 as Weight).saturating_add((8_000 as Weight).saturating_mul(n as Weight))
 	}
 	fn read_write_authority_sets(n: u32) -> Weight {
-		(6_787_000 as Weight)
-			.saturating_add((247_000 as Weight).saturating_mul(n as Weight))
+		(7_677_000 as Weight)
+			.saturating_add((230_000 as Weight).saturating_mul(n as Weight))
 			.saturating_add(RocksDbWeight::get().reads(1 as Weight))
 			.saturating_add(RocksDbWeight::get().writes(1 as Weight))
 	}
-	fn write_authority_sets(n: u32) -> Weight {
-		(3_383_000 as Weight)
-			.saturating_add((99_000 as Weight).saturating_mul(n as Weight))
-			.saturating_add(RocksDbWeight::get().writes(1 as Weight))
-	}
 }