[patch 0/3] nohz_full: only wakeup target CPUs when notifying new tick dependency (v5)

[Marcelo Tosatti]

When enabling per-CPU posix timers, an IPI to nohz_full CPUs might be
performed (to re-read the dependencies and possibly not re-enter
nohz_full on a given CPU).

A common case is for applications that run on nohz_full= CPUs
to not use POSIX timers (eg DPDK). This patch changes the notification
to only IPI the target CPUs where the task(s) whose tick dependencies
are being updated are executing.

This reduces interruptions to nohz_full= CPUs.

v5: actually replace superfluous rcu_read_lock with lockdep_assert
v4: only IPI if the remote task is on the remote runqueue (PeterZ/Frederic)
v3: replace superfluous rcu_read_lock with lockdep_assert (PeterZ)