On Thu, 14 Apr 2011, Tejun Heo wrote:
> On Wed, Apr 13, 2011 at 11:49:51AM -0500, Christoph Lameter wrote:
> > Duh the retry setup if the number overflows is not correct.
> >
> > Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
>
> Can you please repost folded patch with proper [PATCH] subject line
> and cc shaohua.li@xxxxxxxxx so that he can resolve conflicts?
>
> Thanks.
Ok here it is:
From: Christoph Lameter <cl@xxxxxxxxx>
Subject: [PATCH] percpu: preemptless __per_cpu_counter_add
Use this_cpu_cmpxchg to avoid preempt_disable/enable in __percpu_add.
Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
---
lib/percpu_counter.c | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)
Index: linux-2.6/lib/percpu_counter.c
===================================================================
--- linux-2.6.orig/lib/percpu_counter.c 2011-04-13 09:26:19.000000000 -0500
+++ linux-2.6/lib/percpu_counter.c 2011-04-13 09:36:37.000000000 -0500
@@ -71,19 +71,22 @@ EXPORT_SYMBOL(percpu_counter_set);
void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
{
- s64 count;
+ s64 count, new;
- preempt_disable();
- count = __this_cpu_read(*fbc->counters) + amount;
- if (count >= batch || count <= -batch) {
- spin_lock(&fbc->lock);
- fbc->count += count;
- __this_cpu_write(*fbc->counters, 0);
- spin_unlock(&fbc->lock);
- } else {
- __this_cpu_write(*fbc->counters, count);
- }
- preempt_enable();
+ do {
+ count = this_cpu_read(*fbc->counters);
+
+ new = count + amount;
+ /* In case of overflow fold it into the global counter instead */
+ if (new >= batch || new <= -batch) {
+ spin_lock(&fbc->lock);
+ fbc->count += __this_cpu_read(*fbc->counters) + amount;
+ spin_unlock(&fbc->lock);
+ amount = 0;
+ new = 0;
+ }
+
+ } while (this_cpu_cmpxchg(*fbc->counters, count, new) != count);
}
EXPORT_SYMBOL(__percpu_counter_add);
--
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