On Thu, Oct 08, 2020 at 02:35:44PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 07, 2020 at 03:01:53PM -0300, Marcelo Tosatti wrote:
> > Rather than waking up all nohz_full CPUs on the system, only wakeup
> > the target CPUs of member threads of the signal.
> >
> > Reduces interruptions to nohz_full CPUs.
> >
> > Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com>
> >
> > Index: linux-2.6/kernel/time/tick-sched.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/time/tick-sched.c
> > +++ linux-2.6/kernel/time/tick-sched.c
> > @@ -398,7 +398,15 @@ EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_ta
> > */
> > void tick_nohz_dep_set_signal(struct signal_struct *sig, enum
> > tick_dep_bits bit)
> > {
> > - tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
> > + int prev;
> > +
> > + prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask);
> > + if (!prev) {
> > + rcu_read_lock();
> > + for_each_thread(sig, t)
> > + tick_nohz_kick_task(t);
> > + rcu_read_unlock();
> > + }
> > }
>
> AFAICT, and this makes perfect sense, this function is only ever used
> while holding sighand->siglock, which makes the RCU read lock
> superfluous.
>
> Would it make sense to change the signal_struct argument to task_struct,
> such that we can write:
>
> lockdep_assert_held(&p->sighand->siglock);
> for_each_thread(p->signal, t)
> tick_nohz_kick_task(t);
>
> ?
Makes sense, resending -v3.
