Messages in this thread | | | Subject | Re: [PATCH v3 2/2] irqchip/gic-v3-its: Balance initial LPI affinity across CPUs | From | John Garry <> | Date | Fri, 27 Mar 2020 17:52:28 +0000 |
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> + > +/* > + * As suggested by Thomas Gleixner in: > + * https://lore.kernel.org/r/87h80q2aoc.fsf@nanos.tec.linutronix.de > + */ > +static int its_select_cpu(struct irq_data *d, > + const struct cpumask *aff_mask) > +{ > + struct its_device *its_dev = irq_data_get_irq_chip_data(d); > + cpumask_var_t tmpmask; > + int cpu, node; > + > + if (!alloc_cpumask_var(&tmpmask, GFP_KERNEL)) > + return -ENOMEM; > + > + node = its_dev->its->numa_node; > + > + if (!irqd_affinity_is_managed(d)) { > + /* First try the NUMA node */ > + if (node != NUMA_NO_NODE) { > + /* > + * Try the intersection of the affinity mask and the > + * node mask (and the online mask, just to be safe). > + */ > + cpumask_and(tmpmask, cpumask_of_node(node), aff_mask); > + cpumask_and(tmpmask, tmpmask, cpu_online_mask); > + > + /* If that doesn't work, try the nodemask itself */ > + if (cpumask_empty(tmpmask)) > + cpumask_and(tmpmask, cpumask_of_node(node), cpu_online_mask); > + > + cpu = cpumask_pick_least_loaded(d, tmpmask); > + if (cpu < nr_cpu_ids) > + goto out; > + > + /* If we can't cross sockets, give up */ > + if ((its_dev->its->flags & ITS_FLAGS_WORKAROUND_CAVIUM_23144)) > + goto out; > + > + /* If the above failed, expand the search */ > + } > + > + /* Try the intersection of the affinity and online masks */ > + cpumask_and(tmpmask, aff_mask, cpu_online_mask); > + > + /* If that doesn't fly, the online mask is the last resort */ > + if (cpumask_empty(tmpmask)) > + cpumask_copy(tmpmask, cpu_online_mask); > + > + cpu = cpumask_pick_least_loaded(d, tmpmask); > + } else {
Hi Marc,
> + cpumask_and(tmpmask, irq_data_get_affinity_mask(d), cpu_online_mask); > +
Please consider this flow:
- in its_irq_domain_activate()->its_select_cpu(), for a managed interrupt we select the target cpu from the interrupt affin mask
- then in its_set_affinity() call for the same interrupt, we may needlessly reselect the target cpu. This is because in the its_set_affinity()->its_select_cpu() call, we account for that interrupt in the load for the current target cpu, and may find a lesser loaded cpu in the mask and switch.
For example, from mask 0-5 we select cpu0 initially. Then on the 2nd call, we find cpu0 has a greater load (1) then cpu1 (0), and switch to cpu1.
Cheers, John
> + /* If we cannot cross sockets, limit the search to that node */ > + if ((its_dev->its->flags & ITS_FLAGS_WORKAROUND_CAVIUM_23144) && > + node != NUMA_NO_NODE) > + cpumask_and(tmpmask, tmpmask, cpumask_of_node(node)); > + > + cpu = cpumask_pick_least_loaded(d, tmpmask); > + } > +out: > + free_cpumask_var(tmpmask); > + > + pr_debug("IRQ%d -> %*pbl CPU%d\n", d->irq, cpumask_pr_args(aff_mask), cpu); > + return cpu; > +}
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