Re: [PATCH v9 19/32] timers: add_timer_on(): Make sure TIMER_PINNED flag is set

Sebastian Siewior
2023-12-06T10:26:35Z

On 2023-12-06 10:57:57 [+0100], Anna-Maria Behnsen wrote:
> Sebastian Siewior <bigeasy@linutronix.de> writes:
>
> > On 2023-12-01 10:26:41 [+0100], Anna-Maria Behnsen wrote:
> >> When adding a timer to the timer wheel using add_timer_on(), it is an
> >> implicitly pinned timer. With the timer pull at expiry time model in place,
> >> TIMER_PINNED flag is required to make sure timers end up in proper base.
> >>
> >> Add TIMER_PINNED flag unconditionally when add_timer_on() is executed.
> >
> > This is odd. I have some vague memory that this was already the case.
> > Otherwise all add_timer_on() users without TIMER_PINNED may get it wrong
> > due to optimisation.
>
> Which optimisation are you talking about? Are you talking about the
> heuristic for finding the best CPU in get_target_base()? This heuristic
> is not used for add_timer_on().

Yes, true. And nobody probably mixes add_timer_on() and mod_timer().

> Does this makes it a little more clear, why the change is required and
> why it is also valid right now?

Yes, all good. Thanks.

> Thanks,
>
> Anna-Maria

Sebastian