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SubjectRe: [RFC PATCH] virtio-mmio: support for multiple irqs
On Tue, Nov 04, 2014 at 05:35:12PM +0800, Shannon Zhao wrote:
> As the current virtio-mmio only support single irq,
> so some advanced features such as vhost-net with irqfd
> are not supported. And the net performance is not
> the best without vhost-net and irqfd supporting.
>
> This patch support virtio-mmio to request multiple
> irqs like virtio-pci. With this patch and qemu assigning
> multiple irqs for virtio-mmio device, it's ok to use
> vhost-net with irqfd on arm/arm64.
>
> As arm doesn't support msi-x now, we use GSI for
> multiple irq. In this patch we use "vm_try_to_find_vqs"
> to check whether multiple irqs are supported like
> virtio-pci.
>
> Is this the right direction? is there other ways to
> make virtio-mmio support multiple irq? Hope for feedback.
> Thanks.
>
> Signed-off-by: Shannon Zhao <zhaoshenglong@huawei.com>


So how does guest discover whether host device supports multiple IRQs?
Could you please document the new interface?
E.g. send a patch for virtio spec.
I think this really should be controlled by hypervisor, per device.
I'm also tempted to make this a virtio 1.0 only feature.



> ---
> drivers/virtio/virtio_mmio.c | 234 ++++++++++++++++++++++++++++++++++++------
> 1 files changed, 203 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index c600ccf..2b7d935 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -122,6 +122,15 @@ struct virtio_mmio_device {
> /* a list of queues so we can dispatch IRQs */
> spinlock_t lock;
> struct list_head virtqueues;
> +
> + /* multiple irq support */
> + int single_irq_enabled;
> + /* Number of available irqs */
> + unsigned num_irqs;
> + /* Used number of irqs */
> + int used_irqs;
> + /* Name strings for interrupts. */
> + char (*vm_vq_names)[256];
> };
>
> struct virtio_mmio_vq_info {
> @@ -229,33 +238,53 @@ static bool vm_notify(struct virtqueue *vq)
> return true;
> }
>
> +/* Handle a configuration change: Tell driver if it wants to know. */
> +static irqreturn_t vm_config_changed(int irq, void *opaque)
> +{
> + struct virtio_mmio_device *vm_dev = opaque;
> + struct virtio_driver *vdrv = container_of(vm_dev->vdev.dev.driver,
> + struct virtio_driver, driver);
> +
> + if (vdrv && vdrv->config_changed)
> + vdrv->config_changed(&vm_dev->vdev);
> + return IRQ_HANDLED;
> +}
> +
> /* Notify all virtqueues on an interrupt. */
> -static irqreturn_t vm_interrupt(int irq, void *opaque)
> +static irqreturn_t vm_vring_interrupt(int irq, void *opaque)
> {
> struct virtio_mmio_device *vm_dev = opaque;
> struct virtio_mmio_vq_info *info;
> - struct virtio_driver *vdrv = container_of(vm_dev->vdev.dev.driver,
> - struct virtio_driver, driver);
> - unsigned long status;
> + irqreturn_t ret = IRQ_NONE;
> unsigned long flags;
> +
> + spin_lock_irqsave(&vm_dev->lock, flags);
> + list_for_each_entry(info, &vm_dev->virtqueues, node) {
> + if (vring_interrupt(irq, info->vq) == IRQ_HANDLED)
> + ret = IRQ_HANDLED;
> + }
> + spin_unlock_irqrestore(&vm_dev->lock, flags);
> +
> + return ret;
> +}
> +
> +/* Notify all virtqueues and handle a configuration
> + * change on an interrupt. */
> +static irqreturn_t vm_interrupt(int irq, void *opaque)
> +{
> + struct virtio_mmio_device *vm_dev = opaque;
> + unsigned long status;
> irqreturn_t ret = IRQ_NONE;
>
> /* Read and acknowledge interrupts */
> status = readl(vm_dev->base + VIRTIO_MMIO_INTERRUPT_STATUS);
> writel(status, vm_dev->base + VIRTIO_MMIO_INTERRUPT_ACK);
>
> - if (unlikely(status & VIRTIO_MMIO_INT_CONFIG)
> - && vdrv && vdrv->config_changed) {
> - vdrv->config_changed(&vm_dev->vdev);
> - ret = IRQ_HANDLED;
> - }
> + if (unlikely(status & VIRTIO_MMIO_INT_CONFIG))
> + return vm_config_changed(irq, opaque);
>
> - if (likely(status & VIRTIO_MMIO_INT_VRING)) {
> - spin_lock_irqsave(&vm_dev->lock, flags);
> - list_for_each_entry(info, &vm_dev->virtqueues, node)
> - ret |= vring_interrupt(irq, info->vq);
> - spin_unlock_irqrestore(&vm_dev->lock, flags);
> - }
> + if (likely(status & VIRTIO_MMIO_INT_VRING))
> + return vm_vring_interrupt(irq, opaque);
>
> return ret;
> }
> @@ -284,18 +313,98 @@ static void vm_del_vq(struct virtqueue *vq)
> kfree(info);
> }
>
> -static void vm_del_vqs(struct virtio_device *vdev)
> +static void vm_free_irqs(struct virtio_device *vdev)
> {
> + int i;
> struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
> +
> + if (vm_dev->single_irq_enabled) {
> + free_irq(platform_get_irq(vm_dev->pdev, 0), vm_dev);
> + vm_dev->single_irq_enabled = 0;
> + }
> +
> + for (i = 0; i < vm_dev->used_irqs; ++i)
> + free_irq(platform_get_irq(vm_dev->pdev, i), vm_dev);
> +
> + vm_dev->num_irqs = 0;
> + vm_dev->used_irqs = 0;
> + kfree(vm_dev->vm_vq_names);
> + vm_dev->vm_vq_names = NULL;
> +}
> +
> +static void vm_del_vqs(struct virtio_device *vdev)
> +{
> struct virtqueue *vq, *n;
>
> list_for_each_entry_safe(vq, n, &vdev->vqs, list)
> vm_del_vq(vq);
>
> - free_irq(platform_get_irq(vm_dev->pdev, 0), vm_dev);
> + vm_free_irqs(vdev);
> +}
> +
> +static int vm_request_multiple_irqs(struct virtio_device *vdev, int nirqs,
> + bool per_vq_irq)
> +{
> + int err = -ENOMEM;
> + struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
> + unsigned i, v;
> + int irq = 0;
> +
> + vm_dev->num_irqs = nirqs;
> + vm_dev->used_irqs = 0;
> +
> + vm_dev->vm_vq_names = kmalloc_array(nirqs, sizeof(*vm_dev->vm_vq_names),
> + GFP_KERNEL);
> + if (!vm_dev->vm_vq_names)
> + goto error;
> +
> + for (i = 0; i < nirqs; i++) {
> + irq = platform_get_irq(vm_dev->pdev, i);
> + if (irq == -ENXIO)
> + goto error;
> + }
> +
> + /* Set the irq used for configuration */
> + v = vm_dev->used_irqs;
> + snprintf(vm_dev->vm_vq_names[v], sizeof(*vm_dev->vm_vq_names),
> + "%s-config", dev_name(&vdev->dev));
> + irq = platform_get_irq(vm_dev->pdev, v);
> + err = request_irq(irq, vm_config_changed, 0,
> + vm_dev->vm_vq_names[v], vm_dev);
> + ++vm_dev->used_irqs;
> + if (err)
> + goto error;
> +
> + if (!per_vq_irq) {
> + /* Shared irq for all VQs */
> + v = vm_dev->used_irqs;
> + snprintf(vm_dev->vm_vq_names[v], sizeof(*vm_dev->vm_vq_names),
> + "%s-virtqueues", dev_name(&vdev->dev));
> + irq = platform_get_irq(vm_dev->pdev, v);
> + err = request_irq(irq, vm_vring_interrupt, 0,
> + vm_dev->vm_vq_names[v], vm_dev);
> + if (err)
> + goto error;
> + ++vm_dev->used_irqs;
> + }
> + return 0;
> +error:
> + vm_free_irqs(vdev);
> + return err;
> }
>
> +static int vm_request_single_irq(struct virtio_device *vdev)
> +{
> + int err;
> + struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
> + int irq = platform_get_irq(vm_dev->pdev, 0);
>
> + err = request_irq(irq, vm_interrupt, IRQF_SHARED,
> + dev_name(&vdev->dev), vm_dev);
> + if (!err)
> + vm_dev->single_irq_enabled = 1;
> + return err;
> +}
>
> static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned index,
> void (*callback)(struct virtqueue *vq),
> @@ -392,29 +501,92 @@ error_available:
> return ERR_PTR(err);
> }
>
> -static int vm_find_vqs(struct virtio_device *vdev, unsigned nvqs,
> - struct virtqueue *vqs[],
> - vq_callback_t *callbacks[],
> - const char *names[])
> +static int vm_try_to_find_vqs(struct virtio_device *vdev, unsigned nvqs,
> + struct virtqueue *vqs[],
> + vq_callback_t *callbacks[],
> + const char *names[],
> + bool use_multiple_irq,
> + bool per_vq_irq)
> {
> struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
> - unsigned int irq = platform_get_irq(vm_dev->pdev, 0);
> - int i, err;
> + int i, err, nirqs, irq;
> +
> + if (!use_multiple_irq) {
> + /* Old style: one normal interrupt for change and all vqs. */
> + err = vm_request_single_irq(vdev);
> + if (err)
> + goto error_request;
> + } else {
> + if (per_vq_irq) {
> + /* Best option: one for change interrupt, one per vq. */
> + nirqs = 1;
> + for (i = 0; i < nvqs; ++i)
> + if (callbacks[i])
> + ++nirqs;
> + } else {
> + /* Second best: one for change, shared for all vqs. */
> + nirqs = 2;
> + }
>
> - err = request_irq(irq, vm_interrupt, IRQF_SHARED,
> - dev_name(&vdev->dev), vm_dev);
> - if (err)
> - return err;
> + err = vm_request_multiple_irqs(vdev, nirqs, per_vq_irq);
> + if (err)
> + goto error_request;
> + }
>
> - for (i = 0; i < nvqs; ++i) {
> + for (i = 0; i < nvqs; i++) {
> + if (!names[i]) {
> + vqs[i] = NULL;
> + continue;
> + }
> vqs[i] = vm_setup_vq(vdev, i, callbacks[i], names[i]);
> if (IS_ERR(vqs[i])) {
> - vm_del_vqs(vdev);
> - return PTR_ERR(vqs[i]);
> + err = PTR_ERR(vqs[i]);
> + goto error_find;
> + }
> + if (!per_vq_irq || !callbacks[i])
> + continue;
> + /* allocate per-vq irq if available and necessary */
> + snprintf(vm_dev->vm_vq_names[vm_dev->used_irqs],
> + sizeof(*vm_dev->vm_vq_names),
> + "%s-%s",
> + dev_name(&vm_dev->vdev.dev), names[i]);
> + irq = platform_get_irq(vm_dev->pdev, vm_dev->used_irqs);
> + err = request_irq(irq, vring_interrupt, 0,
> + vm_dev->vm_vq_names[vm_dev->used_irqs], vqs[i]);
> + if (err) {
> + vm_del_vq(vqs[i]);
> + goto error_find;
> }
> + ++vm_dev->used_irqs;
> }
> -
> return 0;
> +error_find:
> + vm_del_vqs(vdev);
> +
> +error_request:
> + return err;
> +}
> +
> +static int vm_find_vqs(struct virtio_device *vdev, unsigned nvqs,
> + struct virtqueue *vqs[],
> + vq_callback_t *callbacks[],
> + const char *names[])
> +{
> + int err;
> +
> + /* Try multiple irqs with one irq per queue. */
> + err = vm_try_to_find_vqs(vdev, nvqs, vqs, callbacks, names, true, true);
> + if (!err)
> + return 0;
> + /* Fallback: multiple irqs with one irq for config,
> + * one shared for queues. */
> + err = vm_try_to_find_vqs(vdev, nvqs, vqs, callbacks, names,
> + true, false);
> + if (!err)
> + return 0;
> + /* Finally fall back to regular single interrupts. */
> + return vm_try_to_find_vqs(vdev, nvqs, vqs, callbacks, names,
> + false, false);
> }
>
> static const char *vm_bus_name(struct virtio_device *vdev)
> --
> 1.7.1


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