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// Copyright (C) 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/>.
//! The parachain coretime assignment module.
//!
//! Handles scheduling of assignments coming from the coretime/broker chain. For on-demand
//! assignments it relies on the separate on-demand assignment provider, where it forwards requests
//! to.
//!
//! `CoreDescriptor` contains pointers to the begin and the end of a list of schedules, together
//! with the currently active assignments.
mod mock_helpers;
#[cfg(test)]
mod tests;
use crate::{
configuration, on_demand,
paras::AssignCoretime,
scheduler::common::{Assignment, AssignmentProvider},
ParaId,
};
use alloc::{vec, vec::Vec};
use frame_support::{defensive, pallet_prelude::*};
use frame_system::pallet_prelude::*;
use pallet_broker::CoreAssignment;
use polkadot_primitives::CoreIndex;
use sp_runtime::traits::{One, Saturating};
pub use pallet::*;
/// Fraction expressed as a nominator with an assumed denominator of 57,600.
#[derive(RuntimeDebug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Encode, Decode, TypeInfo)]
pub struct PartsOf57600(u16);
impl PartsOf57600 {
pub const ZERO: Self = Self(0);
pub const FULL: Self = Self(57600);
pub fn new_saturating(v: u16) -> Self {
Self::ZERO.saturating_add(Self(v))
}
pub fn is_full(&self) -> bool {
*self == Self::FULL
}
pub fn saturating_add(self, rhs: Self) -> Self {
let inner = self.0.saturating_add(rhs.0);
if inner > 57600 {
Self(57600)
} else {
Self(inner)
}
}
pub fn saturating_sub(self, rhs: Self) -> Self {
Self(self.0.saturating_sub(rhs.0))
}
pub fn checked_add(self, rhs: Self) -> Option<Self> {
let inner = self.0.saturating_add(rhs.0);
if inner > 57600 {
None
} else {
Some(Self(inner))
}
}
}
/// Assignments as they are scheduled by block number
///
/// for a particular core.
#[derive(Encode, Decode, TypeInfo)]
#[cfg_attr(test, derive(PartialEq, RuntimeDebug))]
struct Schedule<N> {
// Original assignments
assignments: Vec<(CoreAssignment, PartsOf57600)>,
/// When do our assignments become invalid, if at all?
///
/// If this is `Some`, then this `CoreState` will be dropped at that block number. If this is
/// `None`, then we will keep serving our core assignments in a circle until a new set of
/// assignments is scheduled.
end_hint: Option<N>,
/// The next queued schedule for this core.
///
/// Schedules are forming a queue.
next_schedule: Option<N>,
}
/// Descriptor for a core.
///
/// Contains pointers to first and last schedule into `CoreSchedules` for that core and keeps track
/// of the currently active work as well.
#[derive(Encode, Decode, TypeInfo, Default)]
#[cfg_attr(test, derive(PartialEq, RuntimeDebug, Clone))]
struct CoreDescriptor<N> {
/// Meta data about the queued schedules for this core.
queue: Option<QueueDescriptor<N>>,
/// Currently performed work.
current_work: Option<WorkState<N>>,
}
/// Pointers into `CoreSchedules` for a particular core.
///
/// Schedules in `CoreSchedules` form a queue. `Schedule::next_schedule` always pointing to the next
/// item.
#[derive(Encode, Decode, TypeInfo, Copy, Clone)]
#[cfg_attr(test, derive(PartialEq, RuntimeDebug))]
struct QueueDescriptor<N> {
/// First scheduled item, that is not yet active.
first: N,
/// Last scheduled item.
last: N,
}
#[derive(Encode, Decode, TypeInfo)]
#[cfg_attr(test, derive(PartialEq, RuntimeDebug, Clone))]
struct WorkState<N> {
/// Assignments with current state.
///
/// Assignments and book keeping on how much has been served already. We keep track of serviced
/// assignments in order to adhere to the specified ratios.
assignments: Vec<(CoreAssignment, AssignmentState)>,
/// When do our assignments become invalid if at all?
///
/// If this is `Some`, then this `CoreState` will be dropped at that block number. If this is
/// `None`, then we will keep serving our core assignments in a circle until a new set of
/// assignments is scheduled.
end_hint: Option<N>,
/// Position in the assignments we are currently in.
///
/// Aka which core assignment will be popped next on
/// `AssignmentProvider::pop_assignment_for_core`.
pos: u16,
/// Step width
///
/// How much we subtract from `AssignmentState::remaining` for a core served.
step: PartsOf57600,
}
#[derive(Encode, Decode, TypeInfo)]
#[cfg_attr(test, derive(PartialEq, RuntimeDebug, Clone, Copy))]
struct AssignmentState {
/// Ratio of the core this assignment has.
///
/// As initially received via `assign_core`.
ratio: PartsOf57600,
/// How many parts are remaining in this round?
///
/// At the end of each round (in preparation for the next), ratio will be added to remaining.
/// Then every time we get scheduled we subtract a core worth of points. Once we reach 0 or a
/// number lower than what a core is worth (`CoreState::step` size), we move on to the next
/// item in the `Vec`.
///
/// The first round starts with remaining = ratio.
remaining: PartsOf57600,
}
impl<N> From<Schedule<N>> for WorkState<N> {
fn from(schedule: Schedule<N>) -> Self {
let Schedule { assignments, end_hint, next_schedule: _ } = schedule;
let step =
if let Some(min_step_assignment) = assignments.iter().min_by(|a, b| a.1.cmp(&b.1)) {
min_step_assignment.1
} else {
// Assignments empty, should not exist. In any case step size does not matter here:
log::debug!("assignments of a `Schedule` should never be empty.");
PartsOf57600(1)
};
let assignments = assignments
.into_iter()
.map(|(a, ratio)| (a, AssignmentState { ratio, remaining: ratio }))
.collect();
Self { assignments, end_hint, pos: 0, step }
}
}
#[frame_support::pallet]
pub mod pallet {
use super::*;
#[pallet::pallet]
#[pallet::without_storage_info]
pub struct Pallet<T>(_);
#[pallet::config]
pub trait Config: frame_system::Config + configuration::Config + on_demand::Config {}
/// Scheduled assignment sets.
///
/// Assignments as of the given block number. They will go into state once the block number is
/// reached (and replace whatever was in there before).
#[pallet::storage]
pub(super) type CoreSchedules<T: Config> = StorageMap<
_,
Twox256,
(BlockNumberFor<T>, CoreIndex),
Schedule<BlockNumberFor<T>>,
OptionQuery,
>;
/// Assignments which are currently active.
///
/// They will be picked from `PendingAssignments` once we reach the scheduled block number in
/// `PendingAssignments`.
#[pallet::storage]
pub(super) type CoreDescriptors<T: Config> = StorageMap<
_,
Twox256,
CoreIndex,
CoreDescriptor<BlockNumberFor<T>>,
ValueQuery,
GetDefault,
>;
#[pallet::hooks]
impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {}
#[pallet::error]
pub enum Error<T> {
AssignmentsEmpty,
/// assign_core is only allowed to append new assignments at the end of already existing
/// ones or update the last entry.
DisallowedInsert,
}
}
impl<T: Config> AssignmentProvider<BlockNumberFor<T>> for Pallet<T> {
fn pop_assignment_for_core(core_idx: CoreIndex) -> Option<Assignment> {
let now = frame_system::Pallet::<T>::block_number();
CoreDescriptors::<T>::mutate(core_idx, |core_state| {
Self::ensure_workload(now, core_idx, core_state);
let work_state = core_state.current_work.as_mut()?;
// Wrap around:
work_state.pos = work_state.pos % work_state.assignments.len() as u16;
let (a_type, a_state) = &mut work_state
.assignments
.get_mut(work_state.pos as usize)
.expect("We limited pos to the size of the vec one line above. qed");
// advance for next pop:
a_state.remaining = a_state.remaining.saturating_sub(work_state.step);
if a_state.remaining < work_state.step {
// Assignment exhausted, need to move to the next and credit remaining for
// next round.
work_state.pos += 1;
// Reset to ratio + still remaining "credits":
a_state.remaining = a_state.remaining.saturating_add(a_state.ratio);
}
match a_type {
CoreAssignment::Idle => None,
CoreAssignment::Pool => on_demand::Pallet::<T>::pop_assignment_for_core(core_idx),
CoreAssignment::Task(para_id) => Some(Assignment::Bulk((*para_id).into())),
}
})
}
fn report_processed(assignment: Assignment) {
match assignment {
Assignment::Pool { para_id, core_index } =>
on_demand::Pallet::<T>::report_processed(para_id, core_index),
Assignment::Bulk(_) => {},
}
}
/// Push an assignment back to the front of the queue.
///
/// The assignment has not been processed yet. Typically used on session boundaries.
/// Parameters:
/// - `assignment`: The on demand assignment.
fn push_back_assignment(assignment: Assignment) {
match assignment {
Assignment::Pool { para_id, core_index } =>
on_demand::Pallet::<T>::push_back_assignment(para_id, core_index),
Assignment::Bulk(_) => {
// Session changes are rough. We just drop assignments that did not make it on a
// session boundary. This seems sensible as bulk is region based. Meaning, even if
// we made the effort catching up on those dropped assignments, this would very
// likely lead to other assignments not getting served at the "end" (when our
// assignment set gets replaced).
},
}
}
#[cfg(any(feature = "runtime-benchmarks", test))]
fn get_mock_assignment(_: CoreIndex, para_id: polkadot_primitives::Id) -> Assignment {
// Given that we are not tracking anything in `Bulk` assignments, it is safe to always
// return a bulk assignment.
Assignment::Bulk(para_id)
}
fn assignment_duplicated(assignment: &Assignment) {
match assignment {
Assignment::Pool { para_id, core_index } =>
on_demand::Pallet::<T>::assignment_duplicated(*para_id, *core_index),
Assignment::Bulk(_) => {},
}
}
}
impl<T: Config> Pallet<T> {
/// Ensure given workload for core is up to date.
fn ensure_workload(
now: BlockNumberFor<T>,
core_idx: CoreIndex,
descriptor: &mut CoreDescriptor<BlockNumberFor<T>>,
) {
// Workload expired?
if descriptor
.current_work
.as_ref()
.and_then(|w| w.end_hint)
.map_or(false, |e| e <= now)
{
descriptor.current_work = None;
}
let Some(queue) = descriptor.queue else {
// No queue.
return
};
let mut next_scheduled = queue.first;
if next_scheduled > now {
// Not yet ready.
return
}
// Update is needed:
let update = loop {
let Some(update) = CoreSchedules::<T>::take((next_scheduled, core_idx)) else {
break None
};
// Still good?
if update.end_hint.map_or(true, |e| e > now) {
break Some(update)
}
// Move on if possible:
if let Some(n) = update.next_schedule {
next_scheduled = n;
} else {
break None
}
};
let new_first = update.as_ref().and_then(|u| u.next_schedule);
descriptor.current_work = update.map(Into::into);
descriptor.queue = new_first.map(|new_first| {
QueueDescriptor {
first: new_first,
// `last` stays unaffected, if not empty:
last: queue.last,
}
});
}
/// Append another assignment for a core.
///
/// Important: Only appending is allowed or insertion into the last item. Meaning,
/// all already existing assignments must have a `begin` smaller or equal than the one passed
/// here.
/// Updating the last entry is supported to allow for making a core assignment multiple calls to
/// assign_core. Thus if you have too much interlacing for e.g. a single UMP message you can
/// split that up into multiple messages, each triggering a call to `assign_core`, together
/// forming the total assignment.
///
/// Inserting arbitrarily causes a `DispatchError::DisallowedInsert` error.
// With this restriction this function allows for O(1) complexity. It could easily be lifted, if
// need be and in fact an implementation is available
// [here](https://github.com/paritytech/polkadot-sdk/pull/1694/commits/c0c23b01fd2830910cde92c11960dad12cdff398#diff-0c85a46e448de79a5452395829986ee8747e17a857c27ab624304987d2dde8baR386).
// The problem is that insertion complexity then depends on the size of the existing queue,
// which makes determining weights hard and could lead to issues like overweight blocks (at
// least in theory).
pub fn assign_core(
core_idx: CoreIndex,
begin: BlockNumberFor<T>,
mut assignments: Vec<(CoreAssignment, PartsOf57600)>,
end_hint: Option<BlockNumberFor<T>>,
) -> Result<(), DispatchError> {
// There should be at least one assignment.
ensure!(!assignments.is_empty(), Error::<T>::AssignmentsEmpty);
CoreDescriptors::<T>::mutate(core_idx, |core_descriptor| {
let new_queue = match core_descriptor.queue {
Some(queue) => {
ensure!(begin >= queue.last, Error::<T>::DisallowedInsert);
// Update queue if we are appending:
if begin > queue.last {
CoreSchedules::<T>::mutate((queue.last, core_idx), |schedule| {
if let Some(schedule) = schedule.as_mut() {
debug_assert!(schedule.next_schedule.is_none(), "queue.end was supposed to be the end, so the next item must be `None`!");
schedule.next_schedule = Some(begin);
} else {
defensive!("Queue end entry does not exist?");
}
});
}
CoreSchedules::<T>::mutate((begin, core_idx), |schedule| {
let assignments = if let Some(mut old_schedule) = schedule.take() {
old_schedule.assignments.append(&mut assignments);
old_schedule.assignments
} else {
assignments
};
*schedule = Some(Schedule { assignments, end_hint, next_schedule: None });
});
QueueDescriptor { first: queue.first, last: begin }
},
None => {
// Queue empty, just insert:
CoreSchedules::<T>::insert(
(begin, core_idx),
Schedule { assignments, end_hint, next_schedule: None },
);
QueueDescriptor { first: begin, last: begin }
},
};
core_descriptor.queue = Some(new_queue);
Ok(())
})
}
}
impl<T: Config> AssignCoretime for Pallet<T> {
fn assign_coretime(id: ParaId) -> DispatchResult {
let current_block = frame_system::Pallet::<T>::block_number();
// Add a new core and assign the para to it.
let mut config = configuration::ActiveConfig::<T>::get();
let core = config.scheduler_params.num_cores;
config.scheduler_params.num_cores.saturating_inc();
// `assign_coretime` is only called at genesis or by root, so setting the active
// config here is fine.
configuration::Pallet::<T>::force_set_active_config(config);
let begin = current_block + One::one();
let assignment = vec![(pallet_broker::CoreAssignment::Task(id.into()), PartsOf57600::FULL)];
Pallet::<T>::assign_core(CoreIndex(core), begin, assignment, None)
}
}