On Thu, Aug 15, 2019 at 08:02:01PM -0400, Joel Fernandes wrote:
> On Thu, Aug 15, 2019 at 02:45:42PM -0700, Paul E. McKenney wrote:
> > As I understand it, tick_dep_mask forces the tick on globally,
> > ts->tick_dep_mask forces it on for a specific CPU (which RCU uses when it
> > needs a quiescent state from that CPU), current->tick_dep_mask forces
> > it on for a specific task (which RCU uses for callback invocation
> > and certain rcutorture kthreads), and I don't pretend to understand
> > current->signal->tick_dep_mask (the comment says something about POSIX
> > CPU timers).
>
> Right. I am pretty new to all of these so I could have something incorrect in
> a hurry. But thanks for the explanation of your understanding of these.
>
> Yes this commit talks about timers as well for the signal->tick_dep_mask:
> d027d45d8a17 ("nohz: New tick dependency mask")
FWIW, the signal->tick_dep_mask is a thread group wide tick dependency. I'm
not proud of that requirement but we need to keep it for posix CPU timers
that can elapse a timer on all threads of a same process and the tick is
the cheapest way to account for that.
