Re: RFC: sharing config interrupt between virtio devices for saving MSI

Amos Kong
2014-04-27T14:35:41Z

On Sat, Apr 19, 2014 at 12:08:15PM +0800, Amos Kong wrote:
>
> Hi all,
>
> I'm working on this item in Upstream Networking todolist:
>
> | - Sharing config interrupts
> | Support more devices by sharing a single msi vector
> | between multiple virtio devices.
> | (Applies to virtio-blk too).
>
> I have this solution here, and only have draft patches of Solution
> 1 & 2, let's discuss if solution 3 is feasible.
>
> * We should not introduce perf regression in this change
> * little effect is acceptable because we are _sharing_ interrupt
>
> Solution 1:
> ==========
> share one LSI interrupt for configuration change of all virtio devices.
> Draft patch: share_lsi_for_all_config.patch
>
> Solution 2:
> ==========
> share one MSI interrupt for configuration change of all virtio devices.
> Draft patch: share_msix_for_all_config.patch
>
> Solution 3:
> ==========
> dynamic adjust interrupt policy when device is added or removed
> Current:
> -------
> - try to allocate a MSI to device's config
> - try to allocate a MSI for each vq
> - share one MSI for all vqs of one device
> - share one LSI for config & vqs of one device
>
> additional dynamic policies:
> ---------------------------
> - if there is no enough MSI, adjust interrupt allocation for returning
> some MSI
> - try to find a device that allocated one MSI for each vq, change
> it to share one MSI for saving the MSI
> - try to share one MSI for config of all virtio_pci devices
> - try to share one LSI for config of all devices
>
> - if device is removed, try to re-allocate freed MSI to existed
> devices, if they aren't in best status (one MSI for config, one
> MSI for each vq)
> - if config of all devices is sharing one LSI, try to upgrade it to MSI
> - if config of all devices is sharing one MSI, try to allocate one
> MSI for configuration change of each device
> - try to find a device that is sharing one MSI for all vqs, try to
> allocate one MSI for each vq

Hi Michael, Alex

Any thoughts about this ? :)

Thanks, Amos

> diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
> index 101db3f..5ba348d 100644
> --- a/drivers/virtio/virtio_pci.c
> +++ b/drivers/virtio/virtio_pci.c
> @@ -302,6 +302,8 @@ static void vp_free_vectors(struct virtio_device *vdev)
> vp_dev->msix_affinity_masks = NULL;
> }
>
> +//static msix_entry *config_msix_entry;
> +static char config_msix_name[100];
> static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
> bool per_vq_vectors)
> {
> @@ -341,14 +343,13 @@ static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
>
> /* Set the vector used for configuration */
> v = vp_dev->msix_used_vectors;
> - snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
> + snprintf(config_msix_name, sizeof *vp_dev->msix_names,
> "%s-config", name);
> - err = request_irq(vp_dev->msix_entries[v].vector,
> - vp_config_changed, 0, vp_dev->msix_names[v],
> - vp_dev);
> + err = request_irq(vp_dev->pci_dev->irq, vp_config_changed, IRQF_SHARED, config_msix_name, vp_dev);
> if (err)
> goto error;
> - ++vp_dev->msix_used_vectors;
> +
> + //++vp_dev->msix_used_vectors;
>
> iowrite16(v, vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> /* Verify we had enough resources to assign the vector */
> @@ -380,7 +381,7 @@ static int vp_request_intx(struct virtio_device *vdev)
> {
> int err;
> struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> -
> + printk(KERN_INFO "share irq: %d\n", vp_dev->pci_dev->irq);
> err = request_irq(vp_dev->pci_dev->irq, vp_interrupt,
> IRQF_SHARED, dev_name(&vdev->dev), vp_dev);
> if (!err)
> @@ -536,13 +537,13 @@ static int vp_try_to_find_vqs(struct virtio_device *vdev, unsigned nvqs,
> } else {
> if (per_vq_vectors) {
> /* Best option: one for change interrupt, one per vq. */
> - nvectors = 1;
> + nvectors = 0;
> for (i = 0; i < nvqs; ++i)
> if (callbacks[i])
> ++nvectors;
> } else {
> /* Second best: one for change, shared for all vqs. */
> - nvectors = 2;
> + nvectors = 1;
> }
>
> err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors);

> diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
> index 101db3f..5ae1844 100644
> --- a/drivers/virtio/virtio_pci.c
> +++ b/drivers/virtio/virtio_pci.c
> @@ -62,6 +62,8 @@ struct virtio_pci_device
>
> /* Whether we have vector per vq */
> bool per_vq_vectors;
> +
> + char config_msix_name[256];
> };
>
> /* Constants for MSI-X */
> @@ -302,6 +304,8 @@ static void vp_free_vectors(struct virtio_device *vdev)
> vp_dev->msix_affinity_masks = NULL;
> }
>
> +static struct msix_entry *config_msix_entry;
> +static char *config_msix_name;
> static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
> bool per_vq_vectors)
> {
> @@ -309,9 +313,14 @@ static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
> const char *name = dev_name(&vp_dev->vdev.dev);
> unsigned i, v;
> int err = -ENOMEM;
> + int has_config_msix = 1;
>
> - vp_dev->msix_vectors = nvectors;
> + if (!config_msix_entry) {
> + has_config_msix = 0;
> + nvectors += 1;
> + }
>
> + vp_dev->msix_vectors = nvectors;
> vp_dev->msix_entries = kmalloc(nvectors * sizeof *vp_dev->msix_entries,
> GFP_KERNEL);
> if (!vp_dev->msix_entries)
> @@ -341,14 +350,24 @@ static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
>
> /* Set the vector used for configuration */
> v = vp_dev->msix_used_vectors;
> - snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
> +
> + if (has_config_msix == 0) {
> + config_msix_entry = &vp_dev->msix_entries[v];
> + config_msix_name = vp_dev->msix_names[v];
> + } else {
> + config_msix_name = vp_dev->config_msix_name;
> + }
> +
> + snprintf(vp_dev->config_msix_name, sizeof *vp_dev->msix_names,
> "%s-config", name);
> - err = request_irq(vp_dev->msix_entries[v].vector,
> - vp_config_changed, 0, vp_dev->msix_names[v],
> - vp_dev);
> + err = request_irq(config_msix_entry->vector,
> + vp_config_changed, IRQF_SHARED,
> + vp_dev->config_msix_name, vp_dev);
> if (err)
> goto error;
> - ++vp_dev->msix_used_vectors;
> +
> + if (has_config_msix == 0)
> + ++vp_dev->msix_used_vectors;
>
> iowrite16(v, vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> /* Verify we had enough resources to assign the vector */
> @@ -536,13 +555,13 @@ static int vp_try_to_find_vqs(struct virtio_device *vdev, unsigned nvqs,
> } else {
> if (per_vq_vectors) {
> /* Best option: one for change interrupt, one per vq. */
> - nvectors = 1;
> + nvectors = 0;
> for (i = 0; i < nvqs; ++i)
> if (callbacks[i])
> ++nvectors;
> } else {
> /* Second best: one for change, shared for all vqs. */
> - nvectors = 2;
> + nvectors = 1;
> }
>
> err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors);

--
Amos.