refactor: Hoist idle-canister drop in RoundSchedule::start_iteration#10288
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alin-at-dfinity wants to merge 2 commits into
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refactor: Hoist idle-canister drop in RoundSchedule::start_iteration#10288alin-at-dfinity wants to merge 2 commits into
RoundSchedule::start_iteration#10288alin-at-dfinity wants to merge 2 commits into
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Move the "drop idle canisters with 0-100 AP from the subnet schedule" logic out of the `NextExecution::None` branch of the main per-canister loop and into a dedicated pre-loop at the top of `start_iteration`. Behavior is unchanged for canisters that are present in both `canister_states` and `subnet_schedule`: the same set of idle canisters with priorities in the 0-100 AP range get dropped. As a side benefit, the new pre-loop iterates over `subnet_schedule`, so it also cleans up orphan entries for canisters that no longer exist in `canister_states` (those are otherwise pruned by `garbage_collect_subnet_schedule()`, so this is a no-op in practice). Also clarify the doc comment for `IterationSchedule::partition_canisters_to_cores`. This is a small standalone refactor extracted from a larger `CanisterStates` integration, where the main per-canister loop will switch from iterating all canisters to iterating only hot canisters (at which point hoisting becomes a correctness requirement: cold canisters would otherwise no longer be visited by the main loop and their idle entries would not be dropped). Co-authored-by: Cursor <cursoragent@cursor.com>
In `RoundSchedule::start_iteration`, the two calls that construct `CanisterRoundState::new(canister, subnet_schedule.get_mut(*canister_id))` only need a `&CanisterPriority`, so the `get_mut` is purely there for its insertion side effect (it inserts a default entry if the canister is not yet in the schedule). This insertion is redundant: `RoundSchedule::finish_round` calls `subnet_schedule.get_mut(*canister_id)` for every entry in `self.scheduled_canisters` (which is a superset of the canisters that go through these two match arms), and that's the first time anything observes `subnet_schedule.iter()` / `len()`. No code between `start_iteration` and `finish_round` observes the contents of the schedule (the only intermediate reader, `abort_paused_executions_above_limit`, uses `SubnetSchedule::get`, which is tolerant of missing entries). Switch the two read-only sites to `get`. The `get_mut` immediately above (line 333) that decrements rate-limited canisters' AP by 100% stays as is, since it does an actual mutation. Co-authored-by: Cursor <cursoragent@cursor.com>
alin-at-dfinity
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May 22, 2026
| return None; | ||
| } | ||
| CanisterRoundState::new(canister, subnet_schedule.get_mut(*canister_id)) | ||
| CanisterRoundState::new(canister, subnet_schedule.get(canister_id)) |
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FYI: This replacement (and the similar one right below) result in a change in behavior: canisters no longer get a SubnetSchedule entry as soon as they are scheduled by start_iteration().
But this was accidentally left in (during development I had a version of CanisterRoundState::new() that actually mutated the provided CanisterPriority (don't remember why). And finish_round() will call get_mut() to create an entry for all scheduled canisters. And no one looks at the SubnetSchedule in-between.
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Move the "drop idle canisters with 0-100 AP from the subnet schedule" logic out of the
NextExecution::Nonebranch of the main per-canister loop and into a dedicated pre-loop at the top ofstart_iteration. Behavior is unchanged: the same set of idle canisters with priorities in the 0-100 AP range get dropped.Also clarify the doc comment for
IterationSchedule::partition_canisters_to_cores.This is a small standalone refactor extracted from #10287, where the main per-canister loop will switch from iterating all canisters to iterating only hot canisters (at which point hoisting becomes a correctness requirement: cold canisters would otherwise no longer be visited by the main loop and their idle entries would not be dropped).