At 2019-03-26 15:39:54, "Christoph Hellwig" <hch@xxxxxx> wrote:
>Why isn't this using the automatic PCI-level affinity assignment to
>start with?
When enable virtio-blk with multi queues but with only 2 msix-vector.
vp_dev->per_vq_vectors will be false, vp_get_vq_affintity will return NULL directly
so blk_mq_virtio_map_queues will fallback to blk_mq_map_queues.
448 const struct cpumask *vp_get_vq_affinity(struct virtio_device *vdev, int index)
449 {
450 struct virtio_pci_device *vp_dev = to_vp_device(vdev);
451
452 if (!vp_dev->per_vq_vectors ||
453 vp_dev->vqs[index]->msix_vector == VIRTIO_MSI_NO_VECTOR)
454 return NULL;
455
456 return pci_irq_get_affinity(vp_dev->pci_dev,
457 vp_dev->vqs[index]->msix_vector);
458 }
32 int blk_mq_virtio_map_queues(struct blk_mq_queue_map *qmap,
33 struct virtio_device *vdev, int first_vec)
34 {
35 const struct cpumask *mask;
36 unsigned int queue, cpu;
37
38 if (!vdev->config->get_vq_affinity)
39 goto fallback;
40
41 for (queue = 0; queue < qmap->nr_queues; queue++) {
42 mask = vdev->config->get_vq_affinity(vdev, first_vec + queue); //vp_get_vq_affinity return NULL
43 if (!mask)
44 goto fallback;
45
46 for_each_cpu(cpu, mask)
47 qmap->mq_map[cpu] = qmap->queue_offset + queue;
48 }
49
50 return 0;
51 fallback:
52 return blk_mq_map_queues(qmap);
53 }
here is previous discussion
https://patchwork.kernel.org/patch/10865461/
