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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@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: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Lai Jiangshan 2008-07-06 17:23:55 +08:00 committed by Ingo Molnar
parent 5b664cb235
commit 3cac97cbb1
2 changed files with 9 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/rcuclassic.h
View File

@ -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;

22
kernel/rcuclassic.c
View File

@ -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;
rcu_start_batch(rcp);
if (rcu_batch_after(rdp->batch, rcp->pending)) {
rcp->pending = rdp->batch;
rcu_start_batch(rcp);
}
spin_unlock(&rcp->lock);
}
}