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

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Message-ID: <20201026112857.GD104441@lothringen>
Date:   Mon, 26 Oct 2020 12:28:57 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.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 01:45:57AM -0400, Joel Fernandes wrote:
> 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.

Works for me.

Thanks!