Update avail index immediately instead of upon kick: for virtio-net RX this helps parallelism with the host.
Signed-off-by: Michael S. Tsirkin <[email protected]> --- drivers/virtio/virtio_ring.c | 28 +++++++++++++++++++--------- 1 files changed, 19 insertions(+), 9 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index eed5f29..8218fe6 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -89,7 +89,7 @@ struct vring_virtqueue unsigned int num_free; /* Head of free buffer list. */ unsigned int free_head; - /* Number we've added since last sync. */ + /* Number we've added since last kick. */ unsigned int num_added; /* Last used index we've seen. */ @@ -174,6 +174,13 @@ int virtqueue_add_buf_gfp(struct virtqueue *_vq, BUG_ON(data == NULL); + /* Prevent drivers from adding more than num bufs without a kick. */ + if (vq->num_added == vq->vring.num) { + printk(KERN_ERR "gaaa!!!\n"); + END_USE(vq); + return -ENOSPC; + } + /* If the host supports indirect descriptor tables, and we have multiple * buffers, then go indirect. FIXME: tune this threshold */ if (vq->indirect && (out + in) > 1 && vq->num_free) { @@ -227,8 +234,14 @@ add_head: /* Put entry in available array (but don't update avail->idx until they * do sync). FIXME: avoid modulus here? */ - avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num; + avail = vq->vring.avail->idx % vq->vring.num; vq->vring.avail->ring[avail] = head; + vq->num_added++; + + /* Descriptors and available array need to be set before we expose the + * new available array entries. */ + virtio_wmb(); + vq->vring.avail->idx++; pr_debug("Added buffer head %i to %p\n", head, vq); END_USE(vq); @@ -242,17 +255,14 @@ void virtqueue_kick(struct virtqueue *_vq) struct vring_virtqueue *vq = to_vvq(_vq); u16 new, old; START_USE(vq); - /* Descriptors and available array need to be set before we expose the - * new available array entries. */ - virtio_wmb(); - - old = vq->vring.avail->idx; - new = vq->vring.avail->idx = old + vq->num_added; - vq->num_added = 0; /* Need to update avail index before checking if we should notify */ virtio_mb(); + new = vq->vring.avail->idx; + old = new - vq->num_added; + vq->num_added = 0; + if (vq->event ? vring_need_event(vring_avail_event(&vq->vring), new, old) : !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY)) -- 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
