Re: [PATCH 08/18] virtio_ring: support for used_event idx feature
From: Rusty Russell <hidden>
Date: 2011-05-09 04:17:32
Possibly related (same subject, not in this thread)
- 2011-05-15 · Re: [PATCH 08/18] virtio_ring: support for used_event idx feature · "Michael S. Tsirkin" <mst@redhat.com>
On Wed, 4 May 2011 23:51:38 +0300, "Michael S. Tsirkin" [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Add support for the used_event idx feature: when enabling interrupts, publish the current avail index value to the host so that we get interrupts on the next update. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- drivers/virtio/virtio_ring.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-)diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 507d6eb..3a3ed75 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c@@ -320,6 +320,14 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len) ret = vq->data[i]; detach_buf(vq, i); vq->last_used_idx++; + /* If we expect an interrupt for the next entry, tell host + * by writing event index and flush out the write before + * the read in the next get_buf call. */ + if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) { + vring_used_event(&vq->vring) = vq->last_used_idx; + virtio_mb(); + } +
Hmm, so you're still using the avail->flags; it's just if thresholding is enabled the host will ignore it? It's a little subtle, but it keeps this patch small. Perhaps we'll want to make it more explicit later. Thanks, Rusty.