Code Tour

This page maps the main subsystems of Days to the source tree, to make it easier to navigate the codebase.

Entry points

• src/main.rs: CLI entry point (expects a TOML config path).
• src/lib.rs: library root; shared globals (IDs, seed) and module exports.

Topology construction and execution

• src/topos/build.rs: parses topology settings and builds a petgraph UnGraph (FatTree, Torus, or custom edges/hosts).
• src/topos/topo.rs: the main orchestration layer:
  • parses runtime config (threads, duration, mailbox capacity),
  • instantiates switches, schedulers, sources/sinks,
  • computes routes and installs switch forwarding tables,
  • runs the simulation and flushes logs,
  • conditionally wires the PFC link pipeline when enabled.

Switching and forwarding

• src/switches/mod.rs: SchedulingDiscipline enum (selects which scheduler is built per edge).
• src/switches/switch.rs: PacketSwitch (demultiplexes packets using fib / r_fib and forwards via Output<Packet> ports).

Queueing and scheduling (per edge)

• src/schedulers/mod.rs: SchedulerReport and ReportStatistics trait.
• src/schedulers/drop.rs: drop/mark policies (TailDrop, RED, RED_ECN, ECN_THRESHOLD).
• src/schedulers/state.rs: QueueState (shared occupancy tracking, used by PFC).
• src/schedulers/port.rs: FIFO scheduler (Port).
• src/schedulers/drr.rs: Deficit Round Robin.
• src/schedulers/wrr.rs: Weighted Round Robin.
• src/schedulers/wfq.rs: Weighted Fair Queueing.
• src/schedulers/sp.rs: Static Priority.
• src/schedulers/vc.rs: Virtual Clock.

Flows (sources, sinks, routing, collectives)

• src/flows/mod.rs: shared data types (distributions, traffic config, feature-gated DCQCN config).
• src/flows/packet.rs: Packet, ECN field, TCP ACK metadata, control packet markers.
• src/flows/flow.rs: Flow config parsing and path computation.
• src/flows/route.rs: routing implementations (ShortestPath, ECMP, PathFromConfig).
• src/flows/source.rs: PacketSource enum (dispatch wrapper for different sources).
• src/flows/dist_source.rs: packet distribution source.
• src/flows/tcp_source.rs: TCP source (Reno/CUBIC/BBR congestion control, optional app-backed data).
• src/flows/sink.rs: PacketSink enum (dispatch wrapper for different sinks).
• src/flows/basic_sink.rs: basic sink (stats + completion notification).
• src/flows/tcp_sink.rs: TCP sink (ACK generation, ECN echo).
• src/flows/cc.rs: congestion control trait + algorithm selection.
• src/flows/reno.rs, src/flows/cubic.rs, src/flows/bbr.rs: congestion control algorithm implementations.
• src/flows/collective.rs: collective parsing and endpoint generation.
• src/flows/app_source.rs: application-level byte buffers for TCP collectives (actor-based).
• src/flows/wire.rs: optional propagation-delay element (not part of the default topology pipeline).
• src/flows/dcqcn_source.rs, src/flows/dcqcn_sink.rs: DCQCN models (feature dcqcn).

Optional L2 / PFC

• src/l2/frame.rs: LinkFrame (data + optional PFC frames).
• src/l2/link.rs: Link serializer (transmits frames at a configured rate).
• src/l2/pfc.rs: PfcIngressPort + PfcEgressGate and reporting.

Logging, UI, and tracing

• src/utils/logger.rs: CSV logger singleton, report buffering, optional DCQCN event traces.
• src/utils/ui.rs: progress bar UI model.
• src/utils/tracing.rs: concurrency tracking layer and sampler model.

Tests and examples

• tests/: integration tests (often feature-gated via --features test).
• examples/: runnable Rust examples (cargo run --example <name>).