On Sat, Dec 14, 2024 at 12:08:42AM +0100, Frederic Weisbecker wrote:
> Le Thu, Dec 12, 2024 at 10:42:13AM -0800, Paul E. McKenney a écrit :
> > From: Frederic Weisbecker <frederic@xxxxxxxxxx>
> >
> > It's more convenient to benefit from the fallthrough feature of
> > switch / case to handle the timer state machine. Also a new state is
> > about to be added that will take advantage of it.
> >
> > No intended functional change.
> >
> > Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
>
> Please drop this one too. It introduced a subtle (yet desired) behaviour
> change as Boqun noted. I'll resend a better version.
I will drop both on my next rebase. Uladzislau, over to you!
Thanx, Paul
> Thanks!
>
> > ---
> > kernel/rcu/tree_nocb.h | 33 +++++++++++++++++++++++----------
> > 1 file changed, 23 insertions(+), 10 deletions(-)
> >
> > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> > index 2605dd234a13c..0923d60c5a338 100644
> > --- a/kernel/rcu/tree_nocb.h
> > +++ b/kernel/rcu/tree_nocb.h
> > @@ -271,22 +271,35 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
> >
> > raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
> >
> > - /*
> > - * Bypass wakeup overrides previous deferments. In case of
> > - * callback storms, no need to wake up too early.
> > - */
> > - if (waketype == RCU_NOCB_WAKE_LAZY &&
> > - rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
> > - mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush());
> > - WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
> > - } else if (waketype == RCU_NOCB_WAKE_BYPASS) {
> > + switch (waketype) {
> > + case RCU_NOCB_WAKE_BYPASS:
> > + /*
> > + * Bypass wakeup overrides previous deferments. In case of
> > + * callback storms, no need to wake up too early.
> > + */
> > mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
> > WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
> > - } else {
> > + break;
> > + case RCU_NOCB_WAKE_LAZY:
> > + if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
> > + mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush());
> > + WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
> > + }
> > + /*
> > + * If the timer is already armed, a non-lazy enqueue may have happened
> > + * in-between. Don't delay it and fall-through.
> > + */
> > + break;
> > + case RCU_NOCB_WAKE:
> > + fallthrough;
> > + case RCU_NOCB_WAKE_FORCE:
> > if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE)
> > mod_timer(&rdp_gp->nocb_timer, jiffies + 1);
> > if (rdp_gp->nocb_defer_wakeup < waketype)
> > WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
> > + break;
> > + default:
> > + WARN_ON_ONCE(1);
> > }
> >
> > raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
> > --
> > 2.40.1
> >
