linux-kernel - Re: [PATCH 2/9] rcu: Use rcu_segcblist_segempty() instead of open coding it

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Date:   Wed, 5 Jul 2023 14:21:32 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, rcu <rcu@...r.kernel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Giovanni Gherdovich <ggherdovich@...e.cz>
Subject: Re: [PATCH 2/9] rcu: Use rcu_segcblist_segempty() instead of open
 coding it

Le Fri, Jun 02, 2023 at 07:00:00PM -0400, Joel Fernandes a écrit :
> On Wed, May 31, 2023 at 6:17 AM Frederic Weisbecker <frederic@...nel.org> wrote:
> >
> > This makes the code more readable.
> >
> > Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> > ---
> >  kernel/rcu/rcu_segcblist.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
> > index f71fac422c8f..1693ea22ef1b 100644
> > --- a/kernel/rcu/rcu_segcblist.c
> > +++ b/kernel/rcu/rcu_segcblist.c
> > @@ -368,7 +368,7 @@ bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
> >         smp_mb(); /* Ensure counts are updated before callback is entrained. */
> >         rhp->next = NULL;
> >         for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
> > -               if (rsclp->tails[i] != rsclp->tails[i - 1])
> > +               if (!rcu_segcblist_segempty(rsclp, i))
> 
> Hopefully the compiler optimizer will be smart enough to remove this
> from the inlined code ;-):
> if (seg == RCU_DONE_TAIL)
>    return &rsclp->head == rsclp->tails[RCU_DONE_TAIL];

I'm counting on that indeed :-)

> 
> Otherwise it appears to be no functional change for this and the below
> change, and straightforward so for this patch:
> Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>

Thanks.