Re: [PATCH v2 rcu 05/16] rcu: Refactor code a bit in rcu_nocb_do_flush_bypass()

From: Frederic Weisbecker
Date: Wed Nov 23 2022 - 10:59:48 EST


On Mon, Nov 21, 2022 at 05:04:10PM -0800, Paul E. McKenney wrote:
> From: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>
>
> This consolidates the code a bit and makes it cleaner. Functionally it
> is the same.
>
> Reported-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
> kernel/rcu/tree_nocb.h | 17 +++++++++--------
> 1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
> index d6e4c076b0515..213daf81c057f 100644
> --- a/kernel/rcu/tree_nocb.h
> +++ b/kernel/rcu/tree_nocb.h
> @@ -327,10 +327,11 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
> *
> * Note that this function always returns true if rhp is NULL.
> */
> -static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
> +static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp_in,
> unsigned long j, bool lazy)
> {
> struct rcu_cblist rcl;
> + struct rcu_head *rhp = rhp_in;

Why that intermediate rhp_in?

>
> WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp));
> rcu_lockdep_assert_cblist_protected(rdp);
> @@ -345,16 +346,16 @@ static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
>
> /*
> * If the new CB requested was a lazy one, queue it onto the main
> - * ->cblist so we can take advantage of a sooner grade period.
> + * ->cblist so that we can take advantage of the grace-period that will
> + * happen regardless. But queue it onto the bypass list first so that
> + * the lazy CB is ordered with the existing CBs in the bypass list.
> */
> if (lazy && rhp) {
> - rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, NULL);
> - rcu_cblist_enqueue(&rcl, rhp);
> - WRITE_ONCE(rdp->lazy_len, 0);
> - } else {
> - rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
> - WRITE_ONCE(rdp->lazy_len, 0);
> + rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
> + rhp = NULL;
> }
> + rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
> + WRITE_ONCE(rdp->lazy_len, 0);

Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>

Thanks.

>
> rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
> WRITE_ONCE(rdp->nocb_bypass_first, j);
> --
> 2.31.1.189.g2e36527f23
>