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Date: Fri, 3 Feb 2017 15:57:03 +0800
From: Jason Wang <jasowang@...hat.com>
To: Christoph Hellwig <hch@....de>, mst@...hat.com
Cc: axboe@...nel.dk, pbonzini@...hat.com,
virtualization@...ts.linux-foundation.org,
linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] virtio_pci: simplify MSI-X setup
On 2017年01月27日 16:16, Christoph Hellwig wrote:
> 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@....de>
> ---
Reviewed-by: Jason Wang <jasowang@...hat.com>
> 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);
> }
>
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