linux-kernel - Re: [PATCH v9 2/7] rcu/segcblist: Add counters to segcblist datastructure

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Date:   Fri, 6 Nov 2020 19:01:57 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Frederic Weisbecker <frederic@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Marco Elver <elver@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        rcu@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>, fweisbec@...il.com,
        neeraj.iitr10@...il.com
Subject: Re: [PATCH v9 2/7] rcu/segcblist: Add counters to segcblist
 datastructure

On Wed, Nov 04, 2020 at 09:01:33AM -0800, Paul E. McKenney wrote:

> A casual reader might be forgiven for being confused by the combination
> of "Return" in the above comment and the "void" function type below.
> So shouldn't this comment be something like "Add the specified number
> of callbacks to the specified segment..."?

You are right, sorry and will fix it.

> > @@ -330,11 +342,16 @@ void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
> >  
> >  	if (!rcu_segcblist_pend_cbs(rsclp))
> >  		return; /* Nothing to do. */
> > +	rclp->len = rcu_segcblist_get_seglen(rsclp, RCU_WAIT_TAIL) +
> > +		    rcu_segcblist_get_seglen(rsclp, RCU_NEXT_READY_TAIL) +
> > +		    rcu_segcblist_get_seglen(rsclp, RCU_NEXT_TAIL);
> 
> This should be a "for" loop.  Yes, the number and names of the segments
> hasn't changed for a good long time, but nothing like code as above to
> inspire Murphy to more mischief.  :-/
> 
> Actually, why not put the summation in the existing "for" loop below?
> That would save a line of code in addition to providing less inspiration
> for Mr. Murphy.

I can do that. Actually Frederic suggested the same thing but I was reluctant
as I felt it did not give much LOC benefit. Will revisit it.

> 
> >  	*rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
> >  	rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
> >  	WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);
> > -	for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
> > +	for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++) {
> >  		WRITE_ONCE(rsclp->tails[i], rsclp->tails[RCU_DONE_TAIL]);
> > +		rcu_segcblist_set_seglen(rsclp, i, 0);
> > +	}
> >  }
> >  
> >  /*
> > @@ -345,7 +362,6 @@ void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
> >  				struct rcu_cblist *rclp)
> >  {
> >  	rcu_segcblist_add_len(rsclp, rclp->len);
> > -	rclp->len = 0;
> 
> You audited the callers, correct?

Yep.

thanks,

 - Joel