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

[Shannon Zhao <zhaoshenglong@huawei.com>]

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 <zhaoshenglong@huawei.com>
> 
> 
> 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.

	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