On Thu, 27 Jun 2019, Peter Xu wrote:
> + * @TIMER_PINNED: A pinned timer will not be affected by any timer
> + * placement heuristics (like, NOHZ) and will always be run on the CPU
> + * when the timer was enqueued.
s/when/on which/
> + *
> + * Note: Because enqueuing of timers can actually migrate the timer
> + * from one CPU to another, pinned timers are not guaranteed to stay
> + * on the initialy selected CPU. They move to the CPU on which the
> + * enqueue function is invoked via mod_timer() or add_timer(). If the
> + * timer should be placed on a particular CPU, then add_timer_on() has
> + * to be used. It is also suggested that the user should always use
> + * add_timer_on() explicitly for pinned timers.
That last sentence is not correct. add_timer_on() has limitations over
mod_timer(). As pinned prevents the timer from being queued on a remote CPU
mod timer is perfectly fine for many cases.
add_timer_on() is really about queueing a timer on a dedicated CPU, which
is often enough a remote CPU.
Thanks,
tglx
