Re: [REPORT] sched: ITMT + DELAY_DEQUEUE: woken task waits ~1 ms behind another task on the preferred CPU while allowed CPUs are idle

[Francesco Nigro]

On Tue, 2026-11-03 at 18:27 +0100, Mike Galbraith wrote:
> Mmm, that's a be careful what you wish for thing.
[...]
> Not a keeper.

Thanks, that answers my second question for your patch; I had listed
it as earlier work on the same step.

The stalls in the report happen when both busy threads are on CPU 6
at the same time. What the report doesn't show is where the two threads
run the rest of the time. With ITMT on, both run almost only on CPUs 6
and 7, the two highest-ranked of the four: each starts about half of
its bursts on each, and under 3 % on CPUs 4 and 5. With ITMT off, the
two threads' main CPUs differ in every run (run 1: one thread starts
99.9 % of its bursts on CPU 5, the other 100 % on CPU 6). Per-CPU burst
counts from the earlier reproducer (asym_stack2.c), 5 runs of 30 s:
https://github.com/franz1981/itmt-delay-dequeue-repro/blob/49b6d72cb41d2535964c87a660178dd636d1d366/results-final.txt

Is it expected that ITMT keeps two busy threads on the same two
top-ranked CPUs, sometimes on the same one, while the other allowed
CPUs are idle?

Thanks,
Franz