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

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Message-ID: <20201026112445.GC104441@lothringen>
Date:   Mon, 26 Oct 2020 12:24:45 +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 01:40:43AM -0400, Joel Fernandes wrote:
> On Mon, Oct 26, 2020 at 01:32:12AM +0100, Frederic Weisbecker wrote:
> > You seem to have forgotten the suggestion?
> > 
> >     rclp->len += rcu_segcblist_get_seglen(rsclp, i)
> 
> I decided to keep it this way as I did not see how it could be better.
> You mentioned you are Ok with either option so I left it as is.
> 
> Thanks!

Fair enough!

> 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.