linux-kernel - Re: [PATCH v8 2/6] rcu/segcblist: Add counters to segcblist datastructure

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Date:   Mon, 26 Oct 2020 01:45:57 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Marco Elver <elver@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, 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 v8 2/6] rcu/segcblist: Add counters to segcblist
 datastructure

On Mon, Oct 26, 2020 at 01:50:58AM +0100, Frederic Weisbecker wrote:
> On Wed, Oct 21, 2020 at 03:08:09PM -0400, Joel Fernandes (Google) wrote:
> >  bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq)
> >  {
> > -	int i;
> > +	int i, j;
> >  
> >  	WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp));
> >  	if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL))
> > @@ -487,6 +508,10 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq)
> >  	if (rcu_segcblist_restempty(rsclp, i) || ++i >= RCU_NEXT_TAIL)
> >  		return false;
> >  
> > +	/* Accounting: everything below i is about to get merged into i. */
> > +	for (j = i + 1; j <= RCU_NEXT_TAIL; j++)
> > +		rcu_segcblist_move_seglen(rsclp, j, i);
> > +
> 
> Can you perhaps reuse the below loop to move the seglen?

Not easily, because we will need to store 'i' into another variable then, which
does not change.

Besides IMHO, the code is more readable with the loops separated.

thanks,

 - Joel
 

> >  	/*
> >  	 * Merge all later callbacks, including newly arrived callbacks,
> >  	 * into the segment located by the for-loop above.  Assign "seq"