| Scheduler Microbenchmark |
| ######################## |
| |
| This is a scheduler microbenchmark, designed to measure minimum |
| latencies (not scaling performance) of specific low level scheduling |
| primitives independent of overhead from application or API |
| abstractions. It works very simply: a main thread creates a "partner" |
| thread at a higher priority, the partner then sleeps using |
| _pend_curr_irqlock(). From this initial state: |
| |
| 1. The main thread calls _unpend_first_thread() |
| 2. The main thread calls _ready_thread() |
| 3. The main thread calls k_yield() |
| (the kernel switches to the partner thread) |
| 4. The partner thread then runs and calls _pend_curr_irqlock() again |
| (the kernel switches to the main thread) |
| 5. The main thread returns from k_yield() |
| |
| It then iterates this many times, reporting timestamp latencies |
| between each numbered step and for the whole cycle, and a running |
| average for all cycles run. |
| |
| Note that because this involves no timer interaction (except, on some |
| architectures, k_cycle_get_32()), it works correctly when run in QEMU |
| using the -icount argument, which can produce 100% deterministic |
| behavior (not cycle-exact hardware simulation, but exactly N |
| instructions per simulated nanosecond). You can enable this using an |
| environment variable (set at cmake time -- it's not enough to do this |
| for the subsequent make/ninja invocation, cmake needs to see the |
| variable itself): |
| |
| export QEMU_EXTRA_FLAGS="-icount shift=0,align=off,sleep=off" |
