On the recordRead 11 Oct 202621 facts
Days
On the record
- Backend limits
- RED, collectives, and compute stages run only on Scalar and CPU; Metal and CUDA reject those scenarios during validation.days.sh · read 11 Oct 2026
- Collectives
- It supports ring all-reduce and all-gather over TCP, with delay-only compute stages.days.sh · read 4 Oct 2026
- Configuration
- Simulations are configured in a TOML file passed to the command-line program.days.sh · read 4 Oct 2026
- Determinism
- Events are ordered by integer-nanosecond time, phase, sending process, and sequence number, with no floating-point arithmetic in the simulation semantics.days.sh · read 11 Oct 2026
- Execution
- It provides scalar, multicore CPU, Apple Metal, and NVIDIA CUDA backends that aim to produce byte-identical complete simulation states.days.sh · read 11 Oct 2026
- GPU limitation
- RED admission, collectives, and compute stages are supported only on Scalar and CPU; Metal and CUDA reject those scenarios during validation.days.sh · read 4 Oct 2026
- GPU requirements
- CUDA builds require a CUDA 13 toolkit, and Metal runs on Apple GPUs except the M1 family.days.sh · read 11 Oct 2026
- Installation
- The installation guide instructs users to build Days from source with stable Rust and Cargo.days.sh · read 11 Oct 2026
- Intended users
- The site describes using Days to debug simulations, reproduce regressions across backends, and compare other simulators’ approximations against an exact reference.days.sh · read 4 Oct 2026
- License
- The project is licensed under AGPL-3.0-only.github.com · read 11 Oct 2026
- Maker attribution
- The Days site footer credits Baochun Li.days.sh · read 11 Oct 2026
- Network models
- It models fat-tree, torus, dragonfly, and custom graph topologies, along with TCP Reno and CUBIC, rate-paced sources, DCQCN, and CNP.days.sh · read 4 Oct 2026
- Outputs
- By default, Days writes periodic CSV reports for source, sink, and switch statistics; additional traces depend on enabled features.days.sh · read 11 Oct 2026
- Parallel correctness
- The site describes five Lean-proved theorems about the executor’s scheduling model and says backend conformance is checked against the serial result.days.sh · read 4 Oct 2026
- Parallel execution
- The site says five Lean theorems establish that parallel execution reaches the same complete state as canonical serial execution.days.sh · read 11 Oct 2026
- Product
- Days is an exact discrete-event packet network simulator.days.sh · read 4 Oct 2026
- Programming model
- Network elements operate as isolated sequential processes with private state and communicate through timestamped messages.days.sh · read 11 Oct 2026
- Purpose
- Days is an exact discrete-event packet network simulator.days.sh · read 11 Oct 2026
