Messages in this thread | | | Date | Mon, 21 May 2012 10:13:30 +0200 | From | Alexander Gordeev <> | Subject | Re: [PATCH 2/3] x86: x2apic/cluster: Make use of lowest priority delivery mode |
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On Sat, May 19, 2012 at 01:53:36PM -0700, Yinghai Lu wrote: > > +static void > > +x2apic_cluster_vector_allocation_domain(int cpu, struct cpumask *retmask) > > +{ > > + cpumask_copy(retmask, cpu_possible_mask); > > why not using per_cpu(cpus_in_cluster, cpu) instead?
Because it would lead to suboptimal results when updating IRQ affinity:
int __ioapic_set_affinity(struct irq_data *data, const struct cpumask *mask, unsigned int *dest_id) { struct irq_cfg *cfg = data->chip_data;
if (!cpumask_intersects(mask, cpu_online_mask)) return -1;
if (assign_irq_vector(data->irq, data->chip_data, mask)) return -1;
This call ^^^ will update cfg->domain with the value returned by the call to apic->vector_allocation_domain(). If per_cpu(cpus_in_cluster, cpu) is returned as cfg->domain here then all other clusters contained in the 'mask' will not be taken into consideration by the apic->cpu_mask_to_apicid_and() call below.
cpumask_copy(data->affinity, mask);
*dest_id = apic->cpu_mask_to_apicid_and(mask, cfg->domain);
So we really need to submit all possible CPUs here ^^^ to be able finding the best/heaviest cluster out of the 'mask'.
return 0; }
> also you may add one per cpu var like x86_cpu_to_logical_cluster_apicid.
Both cpu_mask_to_apicid() and cpu_mask_to_apicid_and() take a cpumask to derive the apicid from. Even though we could cache the value of apicid in 'x86_cpu_to_logical_cluster_apicid' variable, we still would have to unset CPUs which are not in the requested cpumask. That means scanning through the cpumask etc -- exactly what the the patch does now.
Or I am missing your point here..
> Yinghai
-- Regards, Alexander Gordeev agordeev@redhat.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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