On Wed, Oct 02, 2024 at 04:57:36PM +0200, Frederic Weisbecker wrote:
> 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>
> ---
> 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 97b99cd06923..2fb803f863da 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) {
In the old code, if this "if" branch is not taken,
> - 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 {
... it will end up in this else branch, however,
> + 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;
... here we break instead of fallthrough when waketype ==
RCU_NOCB_WAKE_LAZY and rdp->nocb_defer_wakeup != RCU_NOCB_WAKE_NOT, this
seems to me a functional change, is this intented?
Regards,
Boqun
> + 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);
> --
> 2.46.0
>
