Commit 3cac97cb authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Ingo Molnar
Browse files

rcu classic: simplify the next pending batch 



use a batch number(rcp->pending) instead of a flag(rcp->next_pending)

rcu_start_batch() need to change this flag, so mb()s is needed
for memory-access safe.

but(after this patch applied) rcu_start_batch() do not change
this batch number(rcp->pending), rcp->pending is managed by
__rcu_process_callbacks only, and troublesome mb()s are eliminated.

And codes look simpler and clearer.

Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Gautham Shenoy <ego@in.ibm.com>
Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 5b664cb2

include/linux/rcuclassic.h

+1 −1
Original line number Diff line number Diff line
@@ -45,7 +45,7 @@ 
struct rcu_ctrlblk {

	long	cur;		/* Current batch number.                      */

	long	completed;	/* Number of the last completed batch         */

	int	next_pending;	/* Is the next batch already waiting?         */

	long	pending;	/* Number of the last pending batch           */



	int	signaled;

kernel/rcuclassic.c

+8 −14
Original line number Diff line number Diff line
@@ -60,12 +60,14 @@ EXPORT_SYMBOL_GPL(rcu_lock_map); 
static struct rcu_ctrlblk rcu_ctrlblk = {

	.cur = -300,

	.completed = -300,

	.pending = -300,

	.lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),

	.cpumask = CPU_MASK_NONE,

};

static struct rcu_ctrlblk rcu_bh_ctrlblk = {

	.cur = -300,

	.completed = -300,

	.pending = -300,

	.lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),

	.cpumask = CPU_MASK_NONE,

};
@@ -276,14 +278,8 @@ static void rcu_do_batch(struct rcu_data *rdp) 
 */

static void rcu_start_batch(struct rcu_ctrlblk *rcp)

{

	if (rcp->next_pending &&

	if (rcp->cur != rcp->pending &&

			rcp->completed == rcp->cur) {

		rcp->next_pending = 0;

		/*

		 * next_pending == 0 must be visible in

		 * __rcu_process_callbacks() before it can see new value of cur.

		 */

		smp_wmb();

		rcp->cur++;



		/*
@@ -441,16 +437,14 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, 


		/* determine batch number */

		rdp->batch = rcp->cur + 1;

		/* see the comment and corresponding wmb() in

		 * the rcu_start_batch()

		 */

		smp_rmb();



		if (!rcp->next_pending) {

		if (rcu_batch_after(rdp->batch, rcp->pending)) {

			/* and start it/schedule start if it's a new batch */

			spin_lock(&rcp->lock);

			rcp->next_pending = 1;

			if (rcu_batch_after(rdp->batch, rcp->pending)) {

				rcp->pending = rdp->batch;

				rcu_start_batch(rcp);

			}

			spin_unlock(&rcp->lock);

		}

	}

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