a-b-street/abstreet

Optimize scheduler

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#54 opened on Apr 30, 2020

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 (12 comments) (0 reactions) (0 assignees)Rust (6,779 stars) (256 forks)batch import
good first issue

Description

Profiling reveals https://github.com/dabreegster/abstreet/blob/master/sim/src/scheduler.rs as a hot spot, which makes sense. Anybody have ideas to speed it up? It's a priority queue with updateable priorities. There are lots of alternatives to std::collections::BinaryHeap, but I think I had trouble finding one that was deterministic (given the same inputs, simulations must run exactly the same).

I squeezed running a huge scenario from 71s to 63s using 7a0b9cd09a96e155a26f3304029d7c3ae753a9dc. I bet there's more possible.

Contributor guide

Tech stack
rust
Domain
backendperformance
Issue type
performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Rustpriority queue implementationprofiling
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate alternative priority queue implementations in Rust that maintain determinism. Profile the current scheduler.rs at the mentioned hot spot to identify further optimizations. Explore crates like `priority queue` or `binary heap plus` with custom comparators. Review the linked commit for prior improvements and ensure any changes preserve simulation determinism.