Re: [PATCH v10 18/20] timers: Implement the hierarchical pull model

Anna-Maria Behnsen
2024-02-05T13:29:37Z

Anna-Maria Behnsen <anna-maria@linutronix.de> writes:

> Frederic Weisbecker <frederic@kernel.org> writes:
>
>> Le Thu, Feb 01, 2024 at 05:15:37PM +0100, Anna-Maria Behnsen a écrit :
>>> Frederic Weisbecker <frederic@kernel.org> writes:
>>>
>>> > Le Mon, Jan 15, 2024 at 03:37:41PM +0100, Anna-Maria Behnsen a écrit :
>>> > Heh, I was about to say that it's impossible that timer_base_is_idle()
>>> > at this stage but actually if we run in nohz_full...
>>> >
>>> > It happens so that nohz_full is deactivated until rcutree_online_cpu()
>>> > which calls tick_dep_clear() but it's a pure coincidence that might
>>> > disappear one day. So yes, let's keep it that way.
>>>
>>> I instrumented the code (with NOHZ FULL and NOHZ_IDLE) to make sure the
>>> timer migration hierarchy state 'idle' is in sync with the timer base
>>> 'idle'. And this was one part where it was possible that it runs out of
>>> sync as I remember correctly. But if I understood you correctly, this
>>> shouldn't happen at the moment?
>>
>> Well, it's not supposed to :-)
>
> Hmm, let me double check this and run the tests on the instrumented
> version...

I added a prinkt() to verify what I think I remember. I was able to see
the prints. So it seems, that the coincidence that nohz_full is
deactivated until rcutree_online_cpu() already disappeared.

--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -1672,6 +1672,8 @@ static int tmigr_cpu_online(unsigned int
tmc->idle = timer_base_is_idle();
if (!tmc->idle)
__tmigr_cpu_activate(tmc);
+ else
+ printk("TIMER BASE IS IDLE\n");
tmc->online = true;
raw_spin_unlock_irq(&tmc->lock);
return 0;

Thanks,

Anna-Maria