On Tue, 11 Mar 2014, Amir Vadai wrote:
> +/**
> + * irq_set_mq_dev_affinit_hint - set affinity hint of a queue in multi queue
> + * device
The function is a complete misnomer. It calculates a cpu number and
sets that bit in the supplied cpumask. There is no connection to the
affinity hint at all.
> + * @q: queue index number
> + * @numa_node: prefered numa_node
> + * @affinity_mask: the relevant cpu bit is set according to the policy
> + *
> + * This function sets the affinity_mask according to a numa aware policy.
> + * affinity_mask could be used as an affinity hint for the IRQ related to
> this
> + * queue.
So why is this not directly setting the affinity hint?
> + * The policy is to spread queues across cores - local cores first.
> + *
> + * Returns 0 on success, or a negative error code.
The ENOMEM error code is understandable, but what is the EINVAL for?
> + */
> +int irq_set_mq_dev_affinit_hint(int q, int numa_node,
> + cpumask_t *affinity_mask)
> +{
> + cpumask_var_t mask;
> + int affinity_cpu;
> + int ret = 0;
> +
> + if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
> + return -ENOMEM;
> +
> + q %= num_online_cpus();
> +
> + if (!cpumask_of_node(numa_node)) {
> + cpumask_copy(mask, cpu_online_mask);
> + } else {
> + int n;
> +
> + cpumask_and(mask,
> + cpumask_of_node(numa_node), cpu_online_mask);
> +
> + n = cpumask_weight(mask);
> + if (q >= n) {
> + q -= n;
> + cpumask_andnot(mask, cpu_online_mask, mask);
> + }
This is completely uncommented magic hackery. What is this doing? And
what's the logic here?
If the node does not have enough cpus online to fulfill n > q then you
mask off all online cpus of that node from the online mask and use
some random cpu as target.
And this is true for every q which is larger/equal than the number of cpus
per node.
So lets assume 8 cpus per node and 16 online CPUs. Now you have a card
with 16 queues. So you want to put the first 8 on node 0 and the
second 8 on node 1.
For all q in 0..15
q %= num_online_cpus() -> q
node 0, q 0 -> n = 8 -> cpu 0
node 0, q 1 -> n = 8 -> cpu 1
...
node 7, q 7 -> n = 8 -> cpu 7
So far so good. But
node 1, q 8 -> n = 8 -> cpu 0
node 1, q 9 -> n = 8 -> cpu 1
...
node 1, q 15 -> n = 8 -> cpu 7
I'm not so impressed by the node aware spread.
Thanks,
tglx
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