Re: [PATCH V2 3/4] nvme-pci: avoid irq allocation retrying via .calc_sets

From: Keith Busch
Date: Tue Feb 12 2019 - 10:49:45 EST

On Tue, Feb 12, 2019 at 05:04:38AM -0800, Ming Lei wrote:
> Currently pre-caculate each set vectors, and this way requires same
> 'max_vecs' and 'min_vecs' passed to pci_alloc_irq_vectors_affinity(),
> then nvme_setup_irqs() has to retry in case of allocation failure.
> This usage & interface is a bit awkward because the retry should have
> been avoided by providing one reasonable 'min_vecs'.
> Implement the callback of .calc_sets, so that pci_alloc_irq_vectors_affinity()
> can calculate each set's vector after IRQ vectors is allocated and
> before spread IRQ, then NVMe's retry in case of irq allocation failure
> can be removed.
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>

Thanks, Ming, this whole series looks like a great improvement for
drivers using irq sets.

Minor nit below. Otherwise you may add my review for the whole series
if you spin a v3 for the other minor comments.

Reviewed-by: Keith Busch <keith.busch@xxxxxxxxx>

> +static void nvme_calc_irq_sets(struct irq_affinity *affd, int nvecs)
> +{
> + struct nvme_dev *dev = affd->priv;
> +
> + nvme_calc_io_queues(dev, nvecs);
> +
> + affd->set_vectors[HCTX_TYPE_DEFAULT] = dev->io_queues[HCTX_TYPE_DEFAULT];
> + affd->set_vectors[HCTX_TYPE_READ] = dev->io_queues[HCTX_TYPE_READ];
> + affd->nr_sets = HCTX_TYPE_POLL;
> +}

The value of HCTX_TYPE_POLL happens to be 2, but that seems more of a
coincidence right now. Can we hard code 2 just in case the value changes?