Messages in this thread | | | Date | Wed, 7 Sep 2022 17:38:01 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v5 06/18] rcu: Introduce call_rcu_lazy() API implementation |
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On Wed, Sep 07, 2022 at 09:44:01AM -0400, Joel Fernandes wrote: > Hi Frederic, > > On 9/7/2022 5:40 AM, Frederic Weisbecker wrote: > >> > >> diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > >> index bd8f39ee2cd0..e3344c262672 100644 > >> --- a/kernel/rcu/tree_nocb.h > >> +++ b/kernel/rcu/tree_nocb.h > >> @@ -382,15 +382,19 @@ static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, > >> unsigned long j, unsigned long flush_flags) > >> { > >> bool ret; > >> + bool was_alldone; > >> > >> if (!rcu_rdp_is_offloaded(rdp)) > >> return true; > >> rcu_lockdep_assert_cblist_protected(rdp); > >> rcu_nocb_bypass_lock(rdp); > >> + if (flush_flags & FLUSH_BP_WAKE) > >> + was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); > >> + > > You can check that outside bypass lock (but you still need nocb_lock). > > Right, ok. I can make it outside the bypass lock, and the nocb_lock is implied > by rcu_lockdep_assert_cblist_protected(). > > > > >> ret = rcu_nocb_do_flush_bypass(rdp, rhp, j, flush_flags); > >> > >> - if (flush_flags & FLUSH_BP_WAKE) > >> - wake_nocb_gp(rdp, true); > >> + if (flush_flags & FLUSH_BP_WAKE && was_alldone) > >> + wake_nocb_gp(rdp, false); > > That doesn't check if the bypass list was empty. > > thanks, will add your suggested optimization, however I have a general question: > > For the case where the bypass list is empty, where does rcu_barrier() do a wake > up of the nocb GP thread after entrain()? > > I don't see a call to __call_rcu_nocb_wake() like rcutree_migrate_callbacks() > does. Is the wake up done in some other path?
Actually I can't find it. You're right it may be missing. It's not even just about the bypass list but also the entrain'ed callback. Would you be willing to cook a fix?
Thanks!
> > thanks, > > - Joel
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