HRMP - set DefaultChannelSizeAndCapacityWithSystem with dynamic val…

…ues according to the `ActiveConfig` (#4332)

## Summary
This PR enhances the capability to set
`DefaultChannelSizeAndCapacityWithSystem` for HRMP. Currently, all
testnets (Rococo, Westend) have a hard-coded value set as 'half of the
maximum' determined by the live `ActiveConfig`. While this approach
appears satisfactory, potential issues could arise if the live
`ActiveConfig` are adjusted below these hard-coded values, necessitating
a new runtime release with updated values. Additionally, hard-coded
values have consequences, such as Rococo's benchmarks not functioning:
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/6082656.

## Solution
The proposed solution here is to utilize
`ActiveConfigHrmpChannelSizeAndCapacityRatio`, which reads the current
`ActiveConfig` and calculates `DefaultChannelSizeAndCapacityWithSystem`,
for example, "half of the maximum" based on live data. This way,
whenever `ActiveConfig` is modified,
`ActiveConfigHrmpChannelSizeAndCapacityRatio` automatically returns
adjusted values with the appropriate ratio. Thus, manual adjustments and
new runtime releases become unnecessary.


Relates to a comment/discussion:
https://github.com/paritytech/polkadot-sdk/pull/3721/files#r1541001420
Relates to a comment/discussion:
https://github.com/paritytech/polkadot-sdk/pull/3721/files#r1549291588

---------

Co-authored-by: command-bot <>

polkadot/runtime/parachains/src/configuration.rs

@@ -30,7 +30,7 @@ use primitives::{
 	NodeFeatures, SessionIndex, LEGACY_MIN_BACKING_VOTES, MAX_CODE_SIZE, MAX_HEAD_DATA_SIZE,
 	MAX_POV_SIZE, ON_DEMAND_MAX_QUEUE_MAX_SIZE,
 };
-use sp_runtime::{traits::Zero, Perbill};
+use sp_runtime::{traits::Zero, Perbill, Percent};
 use sp_std::prelude::*;
 
 #[cfg(test)]
@@ -1460,3 +1460,16 @@ impl<T: Config> Pallet<T> {
 		Ok(())
 	}
 }
+
+/// The implementation of `Get<(u32, u32)>` which reads `ActiveConfig` and returns `P` percent of
+/// `hrmp_channel_max_message_size` / `hrmp_channel_max_capacity`.
+pub struct ActiveConfigHrmpChannelSizeAndCapacityRatio<T, P>(sp_std::marker::PhantomData<(T, P)>);
+impl<T: crate::hrmp::pallet::Config, P: Get<Percent>> Get<(u32, u32)>
+	for ActiveConfigHrmpChannelSizeAndCapacityRatio<T, P>
+{
+	fn get() -> (u32, u32) {
+		let config = ActiveConfig::<T>::get();
+		let percent = P::get();
+		(percent * config.hrmp_channel_max_message_size, percent * config.hrmp_channel_max_capacity)
+	}
+}

polkadot/runtime/parachains/src/configuration/tests.rs

@@ -17,7 +17,7 @@
 use super::*;
 use crate::{
 	configuration,
-	mock::{new_test_ext, Configuration, ParasShared, RuntimeOrigin, Test},
+	mock::{new_test_ext, Configuration, MockGenesisConfig, ParasShared, RuntimeOrigin, Test},
 };
 use bitvec::{bitvec, prelude::Lsb0};
 use frame_support::{assert_err, assert_noop, assert_ok};
@@ -547,3 +547,51 @@ fn verify_externally_accessible() {
 		);
 	});
 }
+
+#[test]
+fn active_config_hrmp_channel_size_and_capacity_ratio_works() {
+	frame_support::parameter_types! {
+		pub Ratio100: Percent = Percent::from_percent(100);
+		pub Ratio50: Percent = Percent::from_percent(50);
+	}
+
+	let mut genesis: MockGenesisConfig = Default::default();
+	genesis.configuration.config.hrmp_channel_max_message_size = 1024;
+	genesis.configuration.config.hrmp_channel_max_capacity = 100;
+
+	new_test_ext(genesis).execute_with(|| {
+		let active_config = configuration::ActiveConfig::<Test>::get();
+		assert_eq!(active_config.hrmp_channel_max_message_size, 1024);
+		assert_eq!(active_config.hrmp_channel_max_capacity, 100);
+
+		assert_eq!(
+			ActiveConfigHrmpChannelSizeAndCapacityRatio::<Test, Ratio100>::get(),
+			(1024, 100)
+		);
+		assert_eq!(ActiveConfigHrmpChannelSizeAndCapacityRatio::<Test, Ratio50>::get(), (512, 50));
+
+		// change ActiveConfig
+		assert_ok!(Configuration::set_hrmp_channel_max_message_size(
+			RuntimeOrigin::root(),
+			active_config.hrmp_channel_max_message_size * 4
+		));
+		assert_ok!(Configuration::set_hrmp_channel_max_capacity(
+			RuntimeOrigin::root(),
+			active_config.hrmp_channel_max_capacity * 4
+		));
+		on_new_session(1);
+		on_new_session(2);
+		let active_config = configuration::ActiveConfig::<Test>::get();
+		assert_eq!(active_config.hrmp_channel_max_message_size, 4096);
+		assert_eq!(active_config.hrmp_channel_max_capacity, 400);
+
+		assert_eq!(
+			ActiveConfigHrmpChannelSizeAndCapacityRatio::<Test, Ratio100>::get(),
+			(4096, 400)
+		);
+		assert_eq!(
+			ActiveConfigHrmpChannelSizeAndCapacityRatio::<Test, Ratio50>::get(),
+			(2048, 200)
+		);
+	})
+}

polkadot/runtime/rococo/src/lib.rs

@@ -53,6 +53,7 @@ use runtime_common::{
 use runtime_parachains::{
 	assigner_coretime as parachains_assigner_coretime,
 	assigner_on_demand as parachains_assigner_on_demand, configuration as parachains_configuration,
+	configuration::ActiveConfigHrmpChannelSizeAndCapacityRatio,
 	coretime, disputes as parachains_disputes,
 	disputes::slashing as parachains_slashing,
 	dmp as parachains_dmp, hrmp as parachains_hrmp, inclusion as parachains_inclusion,
@@ -1033,15 +1034,18 @@ impl pallet_message_queue::Config for Runtime {
 impl parachains_dmp::Config for Runtime {}
 
 parameter_types! {
-	pub const DefaultChannelSizeAndCapacityWithSystem: (u32, u32) = (51200, 500);
+	pub const HrmpChannelSizeAndCapacityWithSystemRatio: Percent = Percent::from_percent(100);
 }
 
 impl parachains_hrmp::Config for Runtime {
 	type RuntimeOrigin = RuntimeOrigin;
 	type RuntimeEvent = RuntimeEvent;
 	type ChannelManager = EnsureRoot<AccountId>;
 	type Currency = Balances;
-	type DefaultChannelSizeAndCapacityWithSystem = DefaultChannelSizeAndCapacityWithSystem;
+	type DefaultChannelSizeAndCapacityWithSystem = ActiveConfigHrmpChannelSizeAndCapacityRatio<
+		Runtime,
+		HrmpChannelSizeAndCapacityWithSystemRatio,
+	>;
 	type WeightInfo = weights::runtime_parachains_hrmp::WeightInfo<Runtime>;
 }