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Message-ID: <48708F2B.9030803@cn.fujitsu.com>
Date: Sun, 06 Jul 2008 17:23:55 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Dipankar Sarma <dipankar@...ibm.com>,
Gautham Shenoy <ego@...ibm.com>,
Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [RFC][PATCH 1/2] 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: Lai Jiangshan <laijs@...fujitsu.com>
---
diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
index b3aa05b..5efd734 100644
--- a/include/linux/rcuclassic.h
+++ b/include/linux/rcuclassic.h
@@ -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;
diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
index a38895a..9ac3b94 100644
--- a/kernel/rcuclassic.c
+++ b/kernel/rcuclassic.c
@@ -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++;
/*
@@ -437,16 +433,14 @@ 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;
- rcu_start_batch(rcp);
+ if (rcu_batch_after(rdp->batch, rcp->pending)) {
+ rcp->pending = rdp->batch;
+ rcu_start_batch(rcp);
+ }
spin_unlock(&rcp->lock);
}
}
--
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