linux-kernel - Re: [RFC PATCH 5/5 single-thread-version] implement per-domain single-thread state machine call

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Date:	Thu, 08 Mar 2012 14:04:37 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org
Subject: Re: [RFC PATCH 5/5 single-thread-version] implement per-domain
 single-thread state machine call_srcu()

On Wed, 2012-03-07 at 11:54 +0800, Lai Jiangshan wrote:
> +static void srcu_advance_batches(struct srcu_struct *sp)
> +{
> +       int idx = 1 - (sp->completed & 0x1UL);
> +
> +       /*
> +        * SRCU read-side critical sections are normally short, so check
> +        * twice after a flip.
> +        */
> +       if (!rcu_batch_empty(&sp->batch_check1) ||
> +           !rcu_batch_empty(&sp->batch_check0)) {
> +               if (try_check_zero(sp, idx, 1)) {
> +                       rcu_batch_move(&sp->batch_done, &sp->batch_check1);
> +                       rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
> +                       if (!rcu_batch_empty(&sp->batch_check1)) {
> +                               srcu_flip(sp);
> +                               if (try_check_zero(sp, 1 - idx, 2)) {
> +                                       rcu_batch_move(&sp->batch_done,
> +                                               &sp->batch_check1);
> +                               }
> +                       }
> +               }
> +       }
> +} 

static void srcu_advance_batches(struct srcu_struct *sp)
{
	int idx = 1 - (sp->completed & 1);

	if (rcu_batch_empty(&sp->batch_check0) && 
	    rcu_batch_empty(&sp->batch_check1))
		return;

	if (!try_check_zero(sp, idx, 1))
		return;

	rcu_batch_move(&sp->batch_done,   &sp->batch_check1);
	rcu_batch_move(&sp->batch_check1, &sp->batch_check0);

	if (rcu_batch_empty(&sp->batch_check1))
		return;

	srcu_flip(sp);

	if (!try_check_zero(sp, idx^1, 2))
		return;

	rcu_batch_move(&sp->batch_done, &sp->batch_check1);
}

Seems like a more readable version.. do check I didn't mess up the logic
though.
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