Staking-Async + EPMB: Migrate operations to `poll` #9925

kianenigma · 2025-10-03T12:26:49Z

This PR moves all operations related to staking elections from a mandatory on_initialize with no consideration to weight, to an optional on_poll with accurate, pre-execution weight checking.

Why

on_initialize is a mandatory hook. If a single parachain block happens to contain too many of them, this block can never be authored and imported. In solo/relay chains, this is more forgiving, as you would have one slow block, instead of an indefinite stall.
For example, message-queue XCMs, scheduler and MBMs might overlap with the staking on_initialize in AH (unlikely, but totally possible), and put the chain at risk.
Contrary, poll hooks:
- Might not happen at all by frame-executive (e.g. during MBMs)
- Have access to a clear WeigthMeter, allowing the subject to make a decision about whether to proceed or not.

Functional Changes

As seen by the minimal diff in existing tests, this change, in the absence of weight scarcity, is almost a noop. The only difference is that the start signal from the signed pallet to the verifier pallet is now sent at the end of the signed phase, not the beginning the signed validation.

Non-Functional Changes

Now, the only pallets that call on_poll are multi_block (only the parent, not verifier and signed), and staking_async. This makes the code easier to audit.
Removes a lot of on_initialize terminology from weight functions
Cleans up some stale variations in the mock setup, allowing us to skip the signed pallet's on-initialize. This no longer makes sense as the parent pallet is only one that calls on_poll.

Implementation/Review Notes

Overall Design

The overall idea is to move all operations to a model similar to dispatchables, where before executing f(input) -> Result, we have access to a w(input) -> Weight that gives us the pre-execution weight. If the pre-execution weight is good, we proceed with executing. The execution may override the pre-execution weight to a smaller value if it wishes so.

/// ### Type
///
/// The commonly used `(Weight, Box<dyn Fn() -> Option<Weight>>)` should be interpreted as such:
///
/// * The `Weight` is the pre-computed worst case weight of the operation that we are going to
///   do.
/// * The `Box<dyn Fn() -> Option<Weight>>` is the function that represents that the work that
///   will at most consume the said amount of weight.
///   * Optionally, it can return an updated weight that is more "accurate", based on the
///     execution.
fn per_block_exec(current_phase: Phase<T>) -> (Weight, Box<dyn Fn() -> Option<Weight>>) {
    ...
}

Export Weight

Through this PR, I realized that we previously were never registering the weight of the export process. This is because the export is managed by staking pallet, and previously it had no way to know how much the weight of each export step is.

Now, we alter the ElectionProvider::status interface such that not only we signal if we are ready or not, but also we signal we are ready, and this is the weight of the next elect.

fn status() -> Result<Option<Weight>, ()> {
	match <CurrentPhase<T>>::get() {
		// we're not doing anything.
		Phase::Off => Err(()),

		// we're doing sth but not ready.
		Phase::Signed(_) |
		Phase::SignedValidation(_) |
		Phase::Unsigned(_) |
		Phase::Snapshot(_) |
		Phase::Emergency => Ok(None),

		// we're ready, and this is the weight of the next step
		Phase::Done => Ok(Some(T::WeightInfo::export_non_terminal())),
		Phase::Export(p) =>
			if p.is_zero() {
				Ok(Some(T::WeightInfo::export_terminal()))
			} else {
				Ok(Some(T::WeightInfo::export_non_terminal()))
			},
	}
}

Integration

The only breaking change of this PR is:

impl multi_block::Config for Runtime {
    // .. 
    type Signed = multi_block_signed::Pallet<Self>
}

TODO

Unit tests
Run all papi-integration tests at the end once.
Weight update

…k signed shit

…epmb-poll

paritytech-workflow-stopper · 2025-10-03T13:17:20Z

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/18223135929
Failed job name: cargo-clippy

…epmb-poll

kianenigma · 2025-10-06T10:46:29Z

/cmd bench --help

github-actions · 2025-10-06T10:47:05Z

Command help:

usage: /cmd bench [-h] [--quiet] [--clean] [--image IMAGE]
                  [--runtime [{dev,westend,rococo,asset-hub-westend,asset-hub-rococo,bridge-hub-rococo,bridge-hub-westend,collectives-westend,coretime-rococo,coretime-westend,glutton-westend,people-rococo,people-westend} ...]]
                  [--pallet [PALLET ...]] [--fail-fast]

options:
  -h, --help            show this help message and exit
  --quiet               Won't print start/end/failed messages in PR
  --clean               Clean up the previous bot's & author's comments in PR
  --image IMAGE         Override docker image '--image
                        docker.io/paritytech/ci-unified:latest'
  --runtime [{dev,westend,rococo,asset-hub-westend,asset-hub-rococo,bridge-hub-rococo,bridge-hub-westend,collectives-westend,coretime-rococo,coretime-westend,glutton-westend,people-rococo,people-westend} ...]
                        Runtime(s) space separated
  --pallet [PALLET ...]
                        Pallet(s) space separated
  --fail-fast           Fail fast on first failed benchmark

**Examples**:
 Runs all benchmarks 
 /cmd bench

 Runs benchmarks for pallet_balances and pallet_multisig for all runtimes which have these pallets. **--quiet** makes it to output nothing to PR but reactions
 /cmd bench --pallet pallet_balances pallet_xcm_benchmarks::generic --quiet
 
 Runs bench for all pallets for westend runtime and fails fast on first failed benchmark
 /cmd bench --runtime westend --fail-fast
 
 Does not output anything and cleans up the previous bot's & author command triggering comments in PR 
 /cmd bench --runtime westend rococo --pallet pallet_balances pallet_multisig --quiet --clean

kianenigma · 2025-10-06T10:47:57Z

/cmd bench --pallet pallet_election_provider_multi_block pallet_election_provider_multi_block_signed pallet_election_provider_multi_block_verifier pallet_election_provider_multi_block_unsigned --runtime asset-hub-westend

github-actions · 2025-10-06T10:48:42Z

Command "bench --pallet pallet_election_provider_multi_block pallet_election_provider_multi_block_signed pallet_election_provider_multi_block_verifier pallet_election_provider_multi_block_unsigned --runtime asset-hub-westend" has started 🚀 See logs here

github-actions · 2025-10-06T11:22:15Z

Command "bench --pallet pallet_election_provider_multi_block pallet_election_provider_multi_block_signed pallet_election_provider_multi_block_verifier pallet_election_provider_multi_block_unsigned --runtime asset-hub-westend" has failed ❌! See logs here

andreitrand · 2025-10-06T11:58:36Z

substrate/frame/election-provider-multi-block/src/lib.rs

 //!
+//! ### Phase Transition
+//!
+//! Within all 4 pallets only the parent pallet is allowed to move forward the phases. As of now,


Nit: s/"move forward the phases"/"move the phases forward"/

andreitrand · 2025-10-06T12:06:51Z

substrate/frame/election-provider-multi-block/src/lib.rs

-					_ => T::WeightInfo::on_initialize_nothing(),
-				};
+		fn on_poll(_now: BlockNumberFor<T>, weight_meter: &mut WeightMeter) {
+			// we need current phase to be read in any case -- we can live with it.


Nit: Comment not clear enough, maybe rephrase?

andreitrand · 2025-10-06T12:31:12Z

substrate/frame/election-provider-multi-block/src/lib.rs

-						crate::log!(info, "TESTING: Starting election at block {}", _now);
-						crate::mock::MultiBlock::start().unwrap();
-					}
+			// NOTE: why in here? bc it is more accessible, for example `roll_to_with_ocw`.


Nit: s/bc/because/ (for extra clarity)

andreitrand · 2025-10-06T12:32:54Z

substrate/frame/election-provider-multi-block/src/lib.rs

+	/// * Upon last page of `Phase::Signed`, instruct the `Verifier` to start, if any solution
+	///   exists.
+	///
+	/// What it does not:


Nit: "what it does not do"

andreitrand · 2025-10-06T12:53:21Z

substrate/frame/election-provider-multi-block/src/lib.rs

 			Phase::Off => Err(()),

-			// we're doing sth but not read.
+			// we're doing sth but not ready.


Nit: s/sth/something/

andreitrand · 2025-10-06T12:57:30Z

substrate/frame/election-provider-multi-block/src/signed/tests.rs

 				);

-				// we have 1 block left in signed verification, but we cannot do anything here.
+				// we have 2 block left in signed verification, but we cannot do anything here.


Nit: s/block/blocks/

andreitrand · 2025-10-06T12:58:05Z

substrate/frame/election-provider-multi-block/src/signed/tests.rs


-				// we have 1 block left in signed verification, but we cannot do anything here.
+				// we have 2 block left in signed verification, but we cannot do anything here.
+				// status is not set, as not enough time to do anything.


Nit: (...) as there's not enough time (...)

andreitrand · 2025-10-06T13:00:18Z

substrate/frame/election-provider-multi-block/src/types.rs

-			Self::Export(0) => Self::Off,
-			Self::Export(non_zero_left) =>
-				Self::Export(non_zero_left.defensive_saturating_sub(One::one())),
+			// Export never moves forward via this function, and is always manually set in `elect`


Nit: (...) set in the elect code path.

andreitrand · 2025-10-06T13:11:23Z

substrate/frame/election-provider-multi-block/src/lib.rs

+	///   * Optionally, it can return an updated weight that is more "accurate", based on the
+	///     execution.
+	fn per_block_exec(current_phase: Phase<T>) -> (Weight, Box<dyn Fn() -> Option<Weight>>) {
+		type ExecuteFn = Box<dyn Fn() -> Option<Weight>>;


Since the syntax Box<dyn Fn() -> Option<Weight>> is reused several times in this PR, wouldn't it make sense (for extra clarity) to define it as the type ExecuteFn at the start of the file and then reuse that type alias instead?

andreitrand · 2025-10-06T13:22:25Z

substrate/frame/election-provider-support/src/lib.rs

-	/// called. `Ok(false)` means we are doing something, but work is still ongoing. `elect` should
-	/// not be called. `Ok(true)` means we are done and ready for a call to `elect`.
-	fn status() -> Result<bool, ()>;
+	/// * `Err(())` should signal that we are not doing anything, and `elect` should def. not be


Nit: given the emphasis on it here, I suggest expanding "def." to the full word "definitely".

kianenigma added 12 commits September 23, 2025 18:36

feature in good shape, most tests pass, except those that rely in moc…

52ad11f

…k signed shit

new combinator logic, all tests pass

2608c36

fix benchmarks too

88cb160

move to poll, rename all weights

fac1956

cleanup mock signed stuff

65a2964

staking uses poll now as well

1e4bfc2

tidy up

624e627

fix ahm tests and merge master

f74d49f

solid round of self-review

c05bf0d

Merge branch 'master' of github.com:paritytech/polkadot-sdk into kiz-…

9bcba02

…epmb-poll

remove some todos

10afe31

fmt

0c4289d

kianenigma requested a review from a team as a code owner October 3, 2025 12:26

kianenigma added T2-pallets This PR/Issue is related to a particular pallet. A4-backport-unstable2507 Pull request must be backported to the unstable2507 release branch labels Oct 3, 2025

fix build

5b712bb

sigurpol self-requested a review October 3, 2025 13:21

kianenigma added 2 commits October 6, 2025 11:42

add unit test

7bda95e

Merge branch 'master' of github.com:paritytech/polkadot-sdk into kiz-…

fe82b86

…epmb-poll

andreitrand reviewed Oct 6, 2025

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Staking-Async + EPMB: Migrate operations to poll #9925

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Why

Functional Changes

Non-Functional Changes

Implementation/Review Notes

Overall Design

Export Weight

Integration

TODO

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Staking-Async + EPMB: Migrate operations to `poll` #9925

Staking-Async + EPMB: Migrate operations to `poll` #9925

kianenigma commented Oct 3, 2025 •

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