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Core Concepts

ktstr tests compose from four layers:

  1. Scenarios – what to test: cgroup layout, CPU partitioning, workloads, custom logic.

  2. Flags – which scheduler features to enable for each run.

  3. WorkSpec types – what each worker process does: CPU spin, yield, I/O, bursty patterns, pipe-based IPC.

  4. Checking – how to evaluate results: starvation, fairness, isolation, scheduling gaps, monitor thresholds.

These compose orthogonally. A scenario runs with every valid flag combination, and checks apply uniformly across all runs.

Four supporting concepts complete the picture: Ops and Steps is the primary API for defining scenarios – most tests use CgroupDef and execute_defs from this module. TestTopology provides CPU and LLC layout for cpuset partitioning. Performance Mode applies host-side isolation for noise-sensitive measurements. Resource Budget describes the --cpu-cap tier that coordinates concurrent no-perf-mode VMs and kernel builds via LLC flocks and cgroup v2 cpuset sandboxes.