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Context Lab Mode

context-lab is an isolated scheduler lab mode for exercising real context switches.

Purpose

  • run two dedicated context tasks (ctx-demo-a, ctx-demo-b)
  • perform real switch_context handoffs
  • observe per-task progress counters in logs

Run

cargo run -p kernel --features context-lab

Run with low-level timer IRQ wrapper experiment:

cargo run -p kernel --features irq-exit-wrapper-experimental

Behavior

  • async executor tasks are skipped in lab mode
  • boot enters context-task scheduler directly
  • demo tasks increment counters and call preempt_if_requested()
  • timer IRQ requests reschedule every scheduler quantum
  • timer IRQ records interrupted RIP/RSP for scheduler telemetry
  • timer IRQ frame metadata is validated and exported (irq_frame_invalid, irq_has_rsp, irq_cs, irq_rflags)
  • context handoff occurs at deferred checkpoints when pending IRQ preemption is observed
  • timer IRQ tail preempt hook records forced-preempt attempts/blocks (telemetry-only at this stage)
  • optional low-level IRQ wrapper path can replace the timer interrupt entry/return sequence (experimental)
  • log output includes lines like:
    • ContextLab A=..., B=...
    • Preemptive-groundwork: ... misses=..., watchdog_trips=..., irq_req=..., irq_ckpt=..., irq_forced_attempts=..., irq_forced_blocked=...

Notes

  • This mode is intended for scheduler experimentation.
  • A watchdog panics if no context switch progress is observed for an extended tick window.
  • Default boot path remains unchanged when context-lab is not enabled.