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SubjectRe: [RFC] [PATCH] virtio: Dont add "config" to list for !per_vq_vector
On Wed, Oct 05, 2011 at 11:08:59AM +0530, Krishna Kumar wrote:
> For the MSI but non-per_vq_vector case, the config/change vq
> also gets added to the list of vqs that need to process the
> MSI interrupt. This is not needed as config has it's own
> handler (vp_config_changed). In any case, vring_interrupt()
> finds nothing needs to be done on this vq.
>
> I tested this patch by testing the "Fallback:" and "Finally
> fall back" cases in vp_find_vqs(). Please review.
>
> Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>
(note: this is not a bugfix so not 3.1 material).

> ---
> drivers/virtio/virtio_pci.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff -ruNp org/drivers/virtio/virtio_pci.c new/drivers/virtio/virtio_pci.c
> --- org/drivers/virtio/virtio_pci.c 2011-10-03 09:10:11.000000000 +0530
> +++ new/drivers/virtio/virtio_pci.c 2011-10-04 19:16:34.000000000 +0530
> @@ -415,9 +415,13 @@ static struct virtqueue *setup_vq(struct
> }
> }
>
> - spin_lock_irqsave(&vp_dev->lock, flags);
> - list_add(&info->node, &vp_dev->virtqueues);
> - spin_unlock_irqrestore(&vp_dev->lock, flags);
> + if (callback) {
> + spin_lock_irqsave(&vp_dev->lock, flags);
> + list_add(&info->node, &vp_dev->virtqueues);
> + spin_unlock_irqrestore(&vp_dev->lock, flags);
> + } else {
> + INIT_LIST_HEAD(&info->node);
> + }
>
> return vq;

Some further enhancement suggestions for this shared case:
- we don't really need a lock, do we? and how about replacing vq list
with an array?
- vring_interrupt calls
if (!more_used(vq))
outside any lock.
This looks scary - don't we need a read barrier somewhere?


--
MST


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