Re: [Qemu-devel] [RFC PATCH] virtio-mmio: support for multiple irqs

[Michael S. Tsirkin]

On Thu, Nov 06, 2014 at 05:54:54PM +0800, Shannon Zhao wrote:
> On 2014/11/6 17:34, Michael S. Tsirkin wrote:
> > 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 <address@hidden>
> > 
> > 
> > So how does guest discover whether host device supports multiple IRQs?
> 
> Guest uses vm_try_to_find_vqs to check whether it can get multiple IRQs
> like virtio-pci uses vp_try_to_find_vqs. And within function
> vm_request_multiple_irqs, guest check whether the number of IRQs host
> device gives is equal to the number we want.

OK but how does host specify the number of IRQs for a device?
for pci this is done through the MSI-X capability register.

>       for (i = 0; i < nirqs; i++) {
>               irq = platform_get_irq(vm_dev->pdev, i);
>               if (irq == -ENXIO)
>                       goto error;
>       }
> 
> If we can't get the expected number of IRQs, return error and this try
> fails. Then guest will try two IRQS and single IRQ like virtio-pci.
> 
> > Could you please document the new interface?
> > E.g. send a patch for virtio spec.
> 
> Ok, I'll send it later. Thank you very much :)
> 
> Shannon
> 
> > 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
> > 
> > .
> > 
> 
> 
> -- 
> Shannon