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SubjectRe: [patch v3 3/3] percpu_counter: use atomic64 for counter in SMP
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On Fri, 2011-04-15 at 12:15 +0800, Tejun Heo wrote:
> Hello,
>
> On Thu, Apr 14, 2011 at 10:04:50AM +0800, shaohua.li@intel.com wrote:
> > Index: linux/lib/percpu_counter.c
> > ===================================================================
> > --- linux.orig/lib/percpu_counter.c 2011-04-14 09:53:04.000000000 +0800
> > +++ linux/lib/percpu_counter.c 2011-04-14 10:01:29.000000000 +0800
> > @@ -59,13 +59,17 @@ void percpu_counter_set(struct percpu_co
> > {
> > int cpu;
> >
> > - spin_lock(&fbc->lock);
> > + /*
> > + * Don't really need to disable preempt here, just make sure there is
> > + * no big latency because of preemption
> > + */
> > + preempt_disable();
> > for_each_possible_cpu(cpu) {
> > s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
> > *pcount = 0;
> > }
> > - fbc->count = amount;
> > - spin_unlock(&fbc->lock);
> > + atomic64_set(&fbc->count, amount);
> > + preempt_enable();
>
> Disabling preemption here doesn't make any sense.
> percpu_counter_set() inherently requires its users to guarantee that
> no other user is modifying the percpu counter.
ha, ok.
should I still rebase the patch against Christoph's patch? Looks that
one is still not settled down.




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