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A large part of both suites sleeps and then asserts on the tick counter, either
exactly or within a tick:
tx_thread_sleep(18);
now = tx_time_get();
if ((now == 18) || (now == 19))
The Linux port drives ticks from a thread running under SCHED_FIFO, so ticks
keep arriving whether or not the thread waiting on them can get a core. Starve
that thread and further ticks land between the sleep expiring and the read, the
value is past the one asked for, and a kernel that behaved correctly is reported
as broken. Thirty-five tests here and forty-one on the SMP side sleep and then
consult the clock or a counter driven by it, so this is most of the suite rather
than a corner of it.
The starvation is self-inflicted. Four tests are run at once on a four vCPU
runner, and each one is a process carrying a scheduler thread, a SCHED_FIFO
timer thread and a thread of its own, so the machine is oversubscribed two or
three times over by design. That is why three of these failed in the run of
18 August, and why the retry hid two of them.
Naming the sensitive tests and keeping them apart was tried first and does not
converge. A list covering the tests comparing tx_time_get() for equality missed
threadx_timer_multiple_accuracy_test, which compares timer-driven counters, and
CI failed on it. Widening the list to cover those missed
threadx_thread_sleep_for_100ticks_test, which asserts a range rather than an
equality, and CI failed on that. A list that is quietly incomplete is worse than
no list, because it reads as protection.
So stop overlapping the tests. Serial execution removes the contention for every
test at once, needs nothing to be enumerated, and makes a run reproducible: a
test either passes on its own machine or has a real defect.
The cost, measured in a four CPU cpuset, is close to a factor of four: the
ThreadX suite goes from 12.2 to 47.6 seconds for a configuration and the SMP
suite from 15.2 to 60.0 seconds. The suites parallelise almost perfectly, so
that factor is what parallelism was buying. It is worth giving up. The run this
replaces spent 36 minutes and reported a timeout carrying no information, and
2000 of those seconds went on retrying a test that had already hung twice.
Serial also makes the tick budget in threadx_thread_wait_abort_and_isr_test mean
what it says. Under contention that test took 255 seconds while its 20000 tick
budget never engaged, because the ticks themselves stretch when the process
cannot get a core. With nothing else running, ticks track wall clock and a
budget in ticks bounds elapsed time.
The FreeRTOS suite is left alone. It covers the creation paths of the
compatibility layer and has no tick accuracy tests, so it has nothing to gain
here.
Co-authored-by: Claude Opus 5 (1M context) <[email protected]>
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