[PATCH 4/9] virtio_pci: simplify MSI-X setup

Christoph Hellwig
2017-01-27T08:19:18Z

Try to grab the MSI-X vectors early and fall back to the shared one
before doing lots of allocations.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
drivers/virtio/virtio_pci_common.c | 58 +++++++++++++++++++-------------------
1 file changed, 29 insertions(+), 29 deletions(-)

diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
index 9c4ad7d3f..74ff74c0 100644
--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c
@@ -142,32 +142,39 @@ void vp_del_vqs(struct virtio_device *vdev)
}

static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned nvqs,
- struct virtqueue *vqs[],
- vq_callback_t *callbacks[],
- const char * const names[],
- bool per_vq_vectors)
+ struct virtqueue *vqs[], vq_callback_t *callbacks[],
+ const char * const names[])
{
struct virtio_pci_device *vp_dev = to_vp_device(vdev);
const char *name = dev_name(&vp_dev->vdev.dev);
int i, err = -ENOMEM, allocated_vectors, nvectors;
+ bool shared = false;
u16 msix_vec;

- if (per_vq_vectors) {
- /* Best option: one for change interrupt, one per vq. */
- nvectors = 1;
- for (i = 0; i < nvqs; ++i)
- if (callbacks[i])
- ++nvectors;
- } else {
- /* Second best: one for change, shared for all vqs. */
+ nvectors = 1;
+ for (i = 0; i < nvqs; i++) {
+ if (callbacks[i])
+ nvectors++;
+ }
+
+ /* Try one vector per queue first. */
+ err = pci_alloc_irq_vectors(vp_dev->pci_dev, nvectors, nvectors,
+ PCI_IRQ_MSIX);
+ if (err < 0) {
+ /* Fallback to one vector for config, one shared for queues. */
+ shared = true;
nvectors = 2;
+ err = pci_alloc_irq_vectors(vp_dev->pci_dev, nvectors, nvectors,
+ PCI_IRQ_MSIX);
+ if (err < 0)
+ return err;
}

vp_dev->msix_vectors = nvectors;
vp_dev->msix_names = kmalloc_array(nvectors,
sizeof(*vp_dev->msix_names), GFP_KERNEL);
if (!vp_dev->msix_names)
- return err;
+ goto out_free_irq_vectors;

vp_dev->msix_affinity_masks = kcalloc(nvectors,
sizeof(*vp_dev->msix_affinity_masks), GFP_KERNEL);
@@ -180,18 +187,13 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned nvqs,
goto out_free_msix_affinity_masks;
}

- err = pci_alloc_irq_vectors(vp_dev->pci_dev, nvectors, nvectors,
- PCI_IRQ_MSIX);
- if (err < 0)
- goto out_free_msix_affinity_masks;
-
/* Set the vector used for configuration */
snprintf(vp_dev->msix_names[0], sizeof(*vp_dev->msix_names),
"%s-config", name);
err = request_irq(pci_irq_vector(vp_dev->pci_dev, 0), vp_config_changed,
0, vp_dev->msix_names[0], vp_dev);
if (err)
- goto out_free_irq_vectors;
+ goto out_free_msix_affinity_masks;

/* Verify we had enough resources to assign the vector */
if (vp_dev->config_vector(vp_dev, 0) == VIRTIO_MSI_NO_VECTOR) {
@@ -241,7 +243,11 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned nvqs,
}
vp_dev->msix_vector_map[i] = msix_vec;

- if (per_vq_vectors)
+ /*
+ * Use a different vector for each queue if they are available,
+ * else share the same vector for all VQs.
+ */
+ if (!shared)
allocated_vectors++;
}

@@ -254,8 +260,6 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned nvqs,
vp_dev->config_vector(vp_dev, VIRTIO_MSI_NO_VECTOR);
out_free_config_irq:
free_irq(pci_irq_vector(vp_dev->pci_dev, 0), vp_dev);
-out_free_irq_vectors:
- pci_free_irq_vectors(vp_dev->pci_dev);
out_free_msix_affinity_masks:
for (i = 0; i < nvectors; i++) {
if (vp_dev->msix_affinity_masks[i])
@@ -264,6 +268,8 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned nvqs,
kfree(vp_dev->msix_affinity_masks);
out_free_msix_names:
kfree(vp_dev->msix_names);
+out_free_irq_vectors:
+ pci_free_irq_vectors(vp_dev->pci_dev);
return err;
}

@@ -308,15 +314,9 @@ int vp_find_vqs(struct virtio_device *vdev, unsigned nvqs,
{
int err;

- /* Try MSI-X with one vector per queue. */
- err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, true);
- if (!err)
- return 0;
- /* Fallback: MSI-X with one vector for config, one shared for queues. */
- err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, false);
+ err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names);
if (!err)
return 0;
- /* Finally fall back to regular interrupts. */
return vp_find_vqs_intx(vdev, nvqs, vqs, callbacks, names);
}

--
2.1.4