On Mon, Oct 22, 2012 at 01:10:40PM +0200, Peter Zijlstra wrote:
> On Sat, 2012-10-20 at 21:06 +0200, Andrea Righi wrote:
> > @@ -383,13 +383,7 @@ struct rq {
> > struct list_head leaf_rt_rq_list;
> > #endif
> >
>
> > + unsigned long __percpu *nr_uninterruptible;
>
> This is O(nr_cpus^2) memory..
>
Correct, this doesn't add too much overhead to the wakeup/sleep path,
but it's bad both in terms of memory and performance overhead in the
other parts of the code for large SMP systems.
>
> > +unsigned long nr_uninterruptible_cpu(int cpu)
> > +{
> > + struct rq *this = cpu_rq(cpu);
> > + unsigned long val = 0;
> > + int i;
> > +
> > + for_each_online_cpu(i)
> > + val += per_cpu(*this->nr_uninterruptible, i);
> > +
> > + return val;
> > +}
> >
> >
> I suspect you've got an accounting leak here on hot-plug.
And I think you're right about the accounting leak with cpu hotplug.
I'll do more tests with this part, until I come up with a better idea
in general for the nr_uninterruptible accounting.
Thanks!
-Andrea
> >
> > unsigned long nr_uninterruptible(void)
> > {
> > unsigned long i, sum = 0;
> >
> > for_each_possible_cpu(i)
> > - sum += cpu_rq(i)->nr_uninterruptible;
> > + sum += nr_uninterruptible_cpu(i);
> >
> > /*
> > * Since we read the counters lockless, it might be slightly
>
> And this makes O(n^2) runtime!
>
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