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

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Date:   Tue, 27 Oct 2020 13:30:46 -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 12:24:45PM +0100, Frederic Weisbecker wrote:
[..] 
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 0f23d20d485a..79b7081143a7 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -1160,6 +1160,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
> >   */
> >  static void srcu_invoke_callbacks(struct work_struct *work)
> >  {
> > +	long len;
> >  	bool more;
> >  	struct rcu_cblist ready_cbs;
> >  	struct rcu_head *rhp;
> > @@ -1182,6 +1183,7 @@ static void srcu_invoke_callbacks(struct work_struct *work)
> >  	/* We are on the job!  Extract and invoke ready callbacks. */
> >  	sdp->srcu_cblist_invoking = true;
> >  	rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
> > +	len = ready_cbs.len;
> >  	spin_unlock_irq_rcu_node(sdp);
> >  	rhp = rcu_cblist_dequeue(&ready_cbs);
> >  	for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
> > @@ -1190,13 +1192,14 @@ static void srcu_invoke_callbacks(struct work_struct *work)
> >  		rhp->func(rhp);
> >  		local_bh_enable();
> >  	}
> > +	WARN_ON_ONCE(ready_cbs.len);
> >  
> >  	/*
> >  	 * Update counts, accelerate new callbacks, and if needed,
> >  	 * schedule another round of callback invocation.
> >  	 */
> >  	spin_lock_irq_rcu_node(sdp);
> > -	rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);
> > +	rcu_segcblist_add_len(&sdp->srcu_cblist, -len);
> >  	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
> >  				       rcu_seq_snap(&ssp->srcu_gp_seq));
> >  	sdp->srcu_cblist_invoking = false;
> 
> Looks good! Thanks.

Just to report, with this fix the (s)rcutorture tests pass:

SRCU-N ------- 259086 GPs (143.937/s) [srcu: g3342384 f0x0 total-gps=3342384]
SRCU-P ------- 69443 GPs (38.5794/s) [srcud: g637552 f0x0 total-gps=637552]

thanks,

 - Joel