Messages in this thread | | | From | Joel Fernandes <> | Date | Wed, 18 Oct 2023 10:32:22 -0400 | Subject | Re: [PATCH v3 1/1] rcu: Reduce synchronize_rcu() waiting time |
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On Tue, Oct 17, 2023 at 10:06 AM Uladzislau Rezki <urezki@gmail.com> wrote: [...] > > > + > > > + /* Finally. */ > > > + complete(&rs->completion); > > > +} > > > + > > > +static void rcu_sr_normal_gp_cleanup_work(struct work_struct *work) > > > +{ > > > + struct llist_node *done, *rcu, *next; > > > + > > > + done = llist_del_all(&sr.done); > > > + if (!done) > > > + return; > > > + > > > + llist_for_each_safe(rcu, next, done) > > > + rcu_sr_normal_complete(rcu); > > > +} > > [...] > > > +static void rcu_sr_normal_add_req(struct rcu_synchronize *rs) > > > +{ > > > + atomic_inc(&sr.active); > > > + if (llist_add((struct llist_node *) &rs->head, &sr.curr)) > > > + /* Set the tail. Only first and one user can do that. */ > > > + WRITE_ONCE(sr.curr_tail, (struct llist_node *) &rs->head); > > > + atomic_dec(&sr.active); > > > > Here there is no memory ordering provided by the atomic ops. Is that really Ok? > > > This needs to be reworked since there is no ordering guaranteed. I think > there is a version of "atomic_inc_something" that guarantees it?
Yeah there is atomic_fetch_{inc,dec}{_acquire,_release}()
Or: atomic_inc(&sr.active); smp_mb__after_atomic();
smp_mb__before_atomic(); atomic_dec(&sr.active);
?
That's probably better because we don't need ordering before the inc or after the dec, AFAICS.
I am actually a bit surprised there is no atomic_inc_acquire() yet. :-)
Thanks.
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