Subject: Re: [net-next RFC V4 PATCH 3/4] virtio: introduce a method to get the irq of a specific virtqueue

From: Jason Wang <[email-masked]>
Date: Tue, 26 Jun 2012 13:59:00 +0800

On 06/25/2012 06:14 PM, Michael S. Tsirkin wrote:
> On Mon, Jun 25, 2012 at 05:41:17PM +0800, Jason Wang wrote:
>> Device specific irq optimizations such as irq affinity may be used by virtio
>> drivers. So this patch introduce a new method to get the irq of a specific
>> virtqueue.
>>
>> After this patch, virtio device drivers could query the irq and do device
>> specific optimizations. First user would be virtio-net.
>>
>> Signed-off-by: Jason Wang<[email-masked]>
>> ---
>>   drivers/lguest/lguest_device.c |    8 ++++++++
>>   drivers/s390/kvm/kvm_virtio.c  |    6 ++++++
>>   drivers/virtio/virtio_mmio.c   |    8 ++++++++
>>   drivers/virtio/virtio_pci.c    |   12 ++++++++++++
>>   include/linux/virtio_config.h  |    4 ++++
>>   5 files changed, 38 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
>> index 9e8388e..bcd080f 100644
>> --- a/drivers/lguest/lguest_device.c
>> +++ b/drivers/lguest/lguest_device.c
>> @@ -392,6 +392,13 @@ static const char *lg_bus_name(struct virtio_device *vdev)
>>   	return "";
>>   }
>>
>> +static int lg_get_vq_irq(struct virtio_device *vdev, struct virtqueue *vq)
>> +{
>> +	struct lguest_vq_info *lvq = vq->priv;
>> +
>> +	return lvq->config.irq;
>> +}
>> +
>>   /* The ops structure which hooks everything together. */
>>   static struct virtio_config_ops lguest_config_ops = {
>>   	.get_features = lg_get_features,
>> @@ -404,6 +411,7 @@ static struct virtio_config_ops lguest_config_ops = {
>>   	.find_vqs = lg_find_vqs,
>>   	.del_vqs = lg_del_vqs,
>>   	.bus_name = lg_bus_name,
>> +	.get_vq_irq = lg_get_vq_irq,
>>   };
>>
>>   /*
>> diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
>> index d74e9ae..a897de2 100644
>> --- a/drivers/s390/kvm/kvm_virtio.c
>> +++ b/drivers/s390/kvm/kvm_virtio.c
>> @@ -268,6 +268,11 @@ static const char *kvm_bus_name(struct virtio_device *vdev)
>>   	return "";
>>   }
>>
>> +static int kvm_get_vq_irq(struct virtio_device *vdev, struct virtqueue *vq)
>> +{
>> +	return 0x2603;
>> +}
>> +
>>   /*
>>    * The config ops structure as defined by virtio config
>>    */
>> @@ -282,6 +287,7 @@ static struct virtio_config_ops kvm_vq_configspace_ops = {
>>   	.find_vqs = kvm_find_vqs,
>>   	.del_vqs = kvm_del_vqs,
>>   	.bus_name = kvm_bus_name,
>> +	.get_vq_irq = kvm_get_vq_irq,
>>   };
>>
>>   /*
>> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
>> index f5432b6..2ba37ed 100644
>> --- a/drivers/virtio/virtio_mmio.c
>> +++ b/drivers/virtio/virtio_mmio.c
>> @@ -411,6 +411,13 @@ static const char *vm_bus_name(struct virtio_device *vdev)
>>   	return vm_dev->pdev->name;
>>   }
>>
>> +static int vm_get_vq_irq(struct virtio_device *vdev, struct virtqueue *vq)
>> +{
>> +	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
>> +
>> +	return platform_get_irq(vm_dev->pdev, 0);
>> +}
>> +
>>   static struct virtio_config_ops virtio_mmio_config_ops = {
>>   	.get		= vm_get,
>>   	.set		= vm_set,
>> @@ -422,6 +429,7 @@ static struct virtio_config_ops virtio_mmio_config_ops = {
>>   	.get_features	= vm_get_features,
>>   	.finalize_features = vm_finalize_features,
>>   	.bus_name	= vm_bus_name,
>> +	.get_vq_irq     = vm_get_vq_irq,
>>   };
>>
>>
>> diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
>> index adb24f2..c062227 100644
>> --- a/drivers/virtio/virtio_pci.c
>> +++ b/drivers/virtio/virtio_pci.c
>> @@ -607,6 +607,17 @@ static const char *vp_bus_name(struct virtio_device *vdev)
>>   	return pci_name(vp_dev->pci_dev);
>>   }
>>
>> +static int vp_get_vq_irq(struct virtio_device *vdev, struct virtqueue *vq)
>> +{
>> +	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
>> +	struct virtio_pci_vq_info *info = vq->priv;
>> +
>> +	if (vp_dev->intx_enabled)
>> +		return vp_dev->pci_dev->irq;
>> +	else
>> +		return vp_dev->msix_entries[info->msix_vector].vector;
>> +}
>> +
>>   static struct virtio_config_ops virtio_pci_config_ops = {
>>   	.get		= vp_get,
>>   	.set		= vp_set,
>> @@ -618,6 +629,7 @@ static struct virtio_config_ops virtio_pci_config_ops = {
>>   	.get_features	= vp_get_features,
>>   	.finalize_features = vp_finalize_features,
>>   	.bus_name	= vp_bus_name,
>> +	.get_vq_irq     = vp_get_vq_irq,
>>   };
>>
>>   static void virtio_pci_release_dev(struct device *_d)
>> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
>> index fc457f4..acd6930 100644
>> --- a/include/linux/virtio_config.h
>> +++ b/include/linux/virtio_config.h
>> @@ -98,6 +98,9 @@
>>    *	vdev: the virtio_device
>>    *      This returns a pointer to the bus name a la pci_name from which
>>    *      the caller can then copy.
>> + * @get_vq_irq: get the irq numer of the specific virt queue.
>> + *      vdev: the virtio_device
>> + *      vq: the virtqueue
> What if the vq does not have an IRQ? E.g. control vqs don't.
> What if the IRQ is shared between VQs? Between devices?
> The need to cleanup affinity on destroy is also nasty.
> How about we expose a set_affinity API instead?

Or exposed the irq information such as sharing, level/edge. But I think 
exposing the set_affinity API is enough for multiqueue virtio-net.
> Then:
> 	- non PCI can ignore for now
> 	- with a per vq vector we can force it
> 	- with a shared MSI we make it an OR over all affinities
> 	- with a level interrupt we can ignore it
> 	- on cleanup we can do it in core

Looks good, thanks.
>
>>    */
>>   typedef void vq_callback_t(struct virtqueue *);
>>   struct virtio_config_ops {
>> @@ -116,6 +119,7 @@ struct virtio_config_ops {
>>   	u32 (*get_features)(struct virtio_device *vdev);
>>   	void (*finalize_features)(struct virtio_device *vdev);
>>   	const char *(*bus_name)(struct virtio_device *vdev);
>> +	int (*get_vq_irq)(struct virtio_device *vdev, struct virtqueue *vq);
>>   };
>>
>>   /* If driver didn't advertise the feature, it will never appear. */
>> -- 
>> 1.7.1