On 12 May 2007 20:55:28 +0200 Andi Kleen <[EMAIL PROTECTED]> wrote: > Andrew Morton <[EMAIL PROTECTED]> writes: > > > On Fri, 11 May 2007 10:07:17 -0700 (PDT) > > Christoph Lameter <[EMAIL PROTECTED]> wrote: > > > > > On Fri, 11 May 2007, Andrew Morton wrote: > > > > > > > yipes. percpu_counter_sum() is expensive. > > > > > > Capable of triggering NMI watchdog on 4096+ processors? > > > > Well. That would be a millisecond per cpu which sounds improbable. And > > we'd need to be calling it under local_irq_save() which we presently don't. > > And nobody has reported any problems against the existing callsites. > > > > But it's no speed demon, that's for sure. > > There is one possible optimization for this I did some time ago. You don't > really > need to sum all over the possible map, but only all CPUs that were ever > online. But this only helps on systems where the possible map is bigger > than online map in the common case. But that shouldn't be the case anymore on > x86 > -- it just used to be. If it's true on some other architectures it might > be still worth it. >
hm, yeah. We could put a cpumask in percpu_counter, initialise it to cpu_possible_map. Then, those callsites which have hotplug notifiers can call into new percpu_counter functions which clear and set bits in that cpumask and which drain percpu_counter.counts[cpu] into percpu_counter.count. And percpu_counter_sum() gets taught to do for_each_cpu_mask(fbc->cpumask). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
