Use the new avail_event feature to reduce the number of exits from the guest.
Signed-off-by: Michael S. Tsirkin <[email protected]> --- drivers/virtio/virtio_ring.c | 39 ++++++++++++++++++++++++++++++++++++++- 1 files changed, 38 insertions(+), 1 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 3a3ed75..262dfe6 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -82,6 +82,15 @@ struct vring_virtqueue /* Host supports indirect buffers */ bool indirect; + /* Host publishes avail event idx */ + bool event; + + /* Is kicked_avail below valid? */ + bool kicked_avail_valid; + + /* avail idx value we already kicked. */ + u16 kicked_avail; + /* Number of free buffers */ unsigned int num_free; /* Head of free buffer list. */ @@ -228,6 +237,12 @@ add_head: * new available array entries. */ virtio_wmb(); vq->vring.avail->idx++; + /* If the driver never bothers to kick in a very long while, + * avail index might wrap around. If that happens, invalidate + * kicked_avail index we stored. TODO: make sure all drivers + * kick at least once in 2^16 and remove this. */ + if (unlikely(vq->vring.avail->idx == vq->kicked_avail)) + vq->kicked_avail_valid = true; pr_debug("Added buffer head %i to %p\n", head, vq); END_USE(vq); @@ -236,6 +251,23 @@ add_head: } EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp); + +static bool vring_notify(struct vring_virtqueue *vq) +{ + u16 old, new; + bool v; + if (!vq->event) + return !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY); + + v = vq->kicked_avail_valid; + old = vq->kicked_avail; + new = vq->kicked_avail = vq->vring.avail->idx; + vq->kicked_avail_valid = true; + if (unlikely(!v)) + return true; + return vring_need_event(vring_avail_event(&vq->vring), new, old); +} + void virtqueue_kick(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); @@ -244,7 +276,7 @@ void virtqueue_kick(struct virtqueue *_vq) /* Need to update avail index before checking if we should notify */ virtio_mb(); - if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY)) + if (vring_notify(vq)) /* Prod other side to tell it about changes. */ vq->notify(&vq->vq); @@ -437,6 +469,8 @@ struct virtqueue *vring_new_virtqueue(unsigned int num, vq->vq.name = name; vq->notify = notify; vq->broken = false; + vq->kicked_avail_valid = false; + vq->kicked_avail = 0; vq->last_used_idx = 0; list_add_tail(&vq->vq.list, &vdev->vqs); #ifdef DEBUG @@ -444,6 +478,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int num, #endif vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC); + vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_AVAIL_EVENT_IDX); /* No callback? Tell other side not to bother us. */ if (!callback) @@ -482,6 +517,8 @@ void vring_transport_features(struct virtio_device *vdev) break; case VIRTIO_RING_F_USED_EVENT_IDX: break; + case VIRTIO_RING_F_AVAIL_EVENT_IDX: + break; default: /* We don't understand this bit. */ clear_bit(i, vdev->features); -- 1.7.5.53.gc233e -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
