Re: [PATCHv4 2/2] virtio: refactor find_vqs

["Michael S. Tsirkin" <mst@redhat.com>]

Sorry it took a bit to respond to this.  I kept hoping I'll have time to
test it but looks like I won't before I'm on vacation.  I agree it's
good cleanup, and maybe we can go even further, see below.

On Mon, Aug 10, 2009 at 09:07:52AM +0930, Rusty Russell wrote:
> On Tue, 28 Jul 2009 06:03:08 pm Michael S. Tsirkin wrote:
> > On Tue, Jul 28, 2009 at 12:44:31PM +0930, Rusty Russell wrote:
> > > On Mon, 27 Jul 2009 01:17:09 am Michael S. Tsirkin wrote:
> > > > This refactors find_vqs, making it more readable and robust, and fixing
> > > > two regressions from 2.6.30:
> > > > - double free_irq causing BUG_ON on device removal
> > > > - probe failure when vq can't be assigned to msi-x vector
> > > >   (reported on old host kernels)
> > > > 
> > > > An older version of this patch was tested by Amit Shah.
> > > 
> > > OK, I've applied both of these; I'd like to see a new test by Amit to
> > > make sure tho.
> > > 
> > > I really like this cleanup!  I looked harder at this code, and my best
> > > attempts to untangle it further came to very little.  This is what I
> > > ended up with, but it's all cosmetic and can wait until next merge window.
> > > See what you think.
> > > 
> > > Thanks!
> > > Rusty.
> > > 
> > > virtio_pci: minor MSI-X cleanups
> > > 
> > > 1) Rename vp_request_vectors to vp_request_msix_vectors, and take
> > >    non-MSI-X case out to caller.
> > 
> > I'm not sure this change was for the best: we still have a separate code
> > path under if !use_msix, only in another place now.  See below.
> > And this seems to break the symmetry between request_ and free_vectors.
> 
> Yes, but unfortunately request_vectors was never really symmetrical :(
> 
> That's because we didn't do the request_irq's for the per_vector case, because
> we don't have the names.  This is what prevented me from doing a nice
> encapsulation.

Yes. But let's split free_vectors out into free_msix_vectors and
free_intx as well?

> > > -	err = vp_request_vectors(vdev, nvectors, per_vq_vectors);
> > > +	if (!use_msix) {
> > > +		/* Old style: one normal interrupt for change and all vqs. */
> > > +		vp_dev->msix_vectors = 0;
> > > +		vp_dev->per_vq_vectors = false;
> > > +		err = request_irq(vp_dev->pci_dev->irq, vp_interrupt,
> > > +				  IRQF_SHARED, dev_name(&vdev->dev), vp_dev);
> > > +		if (!err)
> > > +			vp_dev->intx_enabled = 1;
> > 
> > shorter as vp_dev->intx_enabled = !err
> > 
> > > +		return err;
> > 
> > Is that all? Don't we need to create the vqs?
> 
> Oh, yeah :)
> 
> This patch applies on top.  Basically reverts that part, and
> renames vector to msix_vector, which I think makes the code more
> readable.

Yes, I agree, this is good cleanup, structure field names should be
desriptive.  Are you sure we want to make all local variables named
vector renamed to msix_vector though? CodingStyle says local var names
should be short ...  A couple of ideas below.

> virtio: more PCI minor cleanups
> 
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> ---
>  drivers/virtio/virtio_pci.c |   73 +++++++++++++++++++++-----------------------
>  1 file changed, 36 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
> --- a/drivers/virtio/virtio_pci.c
> +++ b/drivers/virtio/virtio_pci.c
> @@ -84,7 +84,7 @@ struct virtio_pci_vq_info
>  	struct list_head node;
>  
>  	/* MSI-X vector (or none) */
> -	unsigned vector;
> +	unsigned msix_vector;

Good. And now we don't need the comment.

>  };
>  
>  /* Qumranet donated their vendor ID for devices 0x1000 thru 0x10FF. */
> @@ -349,7 +349,7 @@ error:
>  static struct virtqueue *setup_vq(struct virtio_device *vdev, unsigned index,
>  				  void (*callback)(struct virtqueue *vq),
>  				  const char *name,
> -				  u16 vector)
> +				  u16 msix_vector)
>  {
>  	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
>  	struct virtio_pci_vq_info *info;
> @@ -374,7 +374,7 @@ static struct virtqueue *setup_vq(struct
>  
>  	info->queue_index = index;
>  	info->num = num;
> -	info->vector = vector;
> +	info->msix_vector = msix_vector;
>  
>  	size = PAGE_ALIGN(vring_size(num, VIRTIO_PCI_VRING_ALIGN));
>  	info->queue = alloc_pages_exact(size, GFP_KERNEL|__GFP_ZERO);
> @@ -398,10 +398,10 @@ static struct virtqueue *setup_vq(struct
>  	vq->priv = info;
>  	info->vq = vq;
>  
> -	if (vector != VIRTIO_MSI_NO_VECTOR) {
> -		iowrite16(vector, vp_dev->ioaddr + VIRTIO_MSI_QUEUE_VECTOR);
> -		vector = ioread16(vp_dev->ioaddr + VIRTIO_MSI_QUEUE_VECTOR);
> -		if (vector == VIRTIO_MSI_NO_VECTOR) {
> +	if (msix_vector != VIRTIO_MSI_NO_VECTOR) {
> +		iowrite16(msix_vector, vp_dev->ioaddr+VIRTIO_MSI_QUEUE_VECTOR);
> +		msix_vector = ioread16(vp_dev->ioaddr+VIRTIO_MSI_QUEUE_VECTOR);

checkpatch will complain that space is lacking around "+".
We won't have a problem if we keep it named vector.

> +		if (msix_vector == VIRTIO_MSI_NO_VECTOR) {
>  			err = -EBUSY;
>  			goto out_assign;
>  		}
> @@ -462,7 +462,8 @@ static void vp_del_vqs(struct virtio_dev
>  	list_for_each_entry_safe(vq, n, &vdev->vqs, list) {
>  		info = vq->priv;
>  		if (vp_dev->per_vq_vectors)
> -			free_irq(vp_dev->msix_entries[info->vector].vector, vq);
> +			free_irq(vp_dev->msix_entries[info->msix_vector].vector,
> +				 vq);
>  		vp_del_vq(vq);
>  	}
>  	vp_dev->per_vq_vectors = false;
> @@ -478,58 +479,56 @@ static int vp_try_to_find_vqs(struct vir
>  			      bool per_vq_vectors)
>  {
>  	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> -	u16 vector;
> +	u16 msix_vector;
>  	int i, err, nvectors, allocated_vectors;
>  
>  	if (!use_msix) {
>  		/* Old style: one normal interrupt for change and all vqs. */
>  		vp_dev->msix_vectors = 0;
> -		vp_dev->per_vq_vectors = false;

I know it's enough to look at msix_vectors, but isn't
it cleaner to have per_vq_vectors consistent as well?
E.g. del_vqs seems to only look at per_vq_vectors.

>  		err = request_irq(vp_dev->pci_dev->irq, vp_interrupt,
>  				  IRQF_SHARED, dev_name(&vdev->dev), vp_dev);
> -		if (!err)
> -			vp_dev->intx_enabled = 1;
> -		return err;
> +		if (err)
> +			return err;

Maybe move this part out into a separate function?  This way
vp_try_to_find_vqs does high-level processing.


> +	} else {
> +		if (per_vq_vectors) {
> +			/* Best option: one for change interrupt, one per vq. */
> +			nvectors = 1;
> +			for (i = 0; i < nvqs; ++i)
> +				if (callbacks[i])
> +					++nvectors;
> +		} else {
> +			/* Second best: one for change, shared for all vqs. */
> +			nvectors = 2;

Out of curiosity: why do you put {} here? They aren't
strictly necessary ...

> +		}
> +
> +		err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors);
> +		if (err)
> +			goto error_request;
>  	}
>  
> -	if (per_vq_vectors) {
> -		/* Best option: one for change interrupt, one per vq. */
> -		nvectors = 1;
> -		for (i = 0; i < nvqs; ++i)
> -			if (callbacks[i])
> -				++nvectors;
> -	} else {
> -		/* Second best: one for change, shared one for all vqs. */
> -		nvectors = 2;
> -	}
> -
> -	err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors);
> -	if (err)
> -		goto error_request;
> -
>  	vp_dev->per_vq_vectors = per_vq_vectors;
>  	allocated_vectors = vp_dev->msix_used_vectors;
>  	for (i = 0; i < nvqs; ++i) {
>  		if (!callbacks[i] || !vp_dev->msix_enabled)
> -			vector = VIRTIO_MSI_NO_VECTOR;
> +			msix_vector = VIRTIO_MSI_NO_VECTOR;
>  		else if (vp_dev->per_vq_vectors)
> -			vector = allocated_vectors++;
> +			msix_vector = allocated_vectors++;
>  		else
> -			vector = VP_MSIX_VQ_VECTOR;
> -		vqs[i] = setup_vq(vdev, i, callbacks[i], names[i], vector);
> +			msix_vector = VP_MSIX_VQ_VECTOR;
> +		vqs[i] = setup_vq(vdev, i, callbacks[i], names[i], msix_vector);
>  		if (IS_ERR(vqs[i])) {
>  			err = PTR_ERR(vqs[i]);
>  			goto error_find;
>  		}
>  		/* allocate per-vq irq if available and necessary */
> -		if (vp_dev->per_vq_vectors && vector != VIRTIO_MSI_NO_VECTOR) {
> -			snprintf(vp_dev->msix_names[vector],
> +		if (vp_dev->per_vq_vectors) {
> +			snprintf(vp_dev->msix_names[msix_vector],
>  				 sizeof *vp_dev->msix_names,
>  				 "%s-%s",
>  				 dev_name(&vp_dev->vdev.dev), names[i]);
> -			err = request_irq(vp_dev->msix_entries[vector].vector,
> -					  vring_interrupt, 0,
> -					  vp_dev->msix_names[vector], vqs[i]);
> +			err = request_irq(msix_vector, vring_interrupt, 0,
> +					  vp_dev->msix_names[msix_vector],
> +					  vqs[i]);
>  			if (err) {
>  				vp_del_vq(vqs[i]);
>  				goto error_find;