[dpdk-dev] [PATCH v2 1/4] net/virtio: fix queue flushing with vector Rx enabled

[Tiwei Bie]

On Fri, Jan 19, 2018 at 04:55:53PM +0100, Olivier Matz wrote:
> When using vector Rx mode (use_simple_rx = 1), vq->vq_descx[] is not
> kept up to date. To properly detach the mbufs in this case, browse
> sw_ring[] instead, as it's done in virtqueue_rxvq_flush().
> 
> Since we need virtio_get_queue_type(), also move this function in
> virtqueue.h as a static inline.
> 
> Fixes: fc3d66212fed ("virtio: add vector Rx")
> Cc: stable at dpdk.org
> 
> Signed-off-by: Olivier Matz <olivier.matz at 6wind.com>
> ---
> 
> Tiwei,
> 
> While it passes my test plan, please carefully check that what I did in
> virtqueue_detatch_unused() is correct. I tried to reproduce what is done
> in virtqueue_rxvq_flush(), but I may be mistaking due to the different
> ring layout assumption and mbuf management between standard and vector.
> 
> Thanks
> Olivier
> 
> 
>  drivers/net/virtio/virtio_ethdev.c | 11 -----------
>  drivers/net/virtio/virtqueue.c     | 17 +++++++++++++++--
>  drivers/net/virtio/virtqueue.h     | 11 +++++++++++
>  3 files changed, 26 insertions(+), 13 deletions(-)
> 
[...]
>  struct rte_mbuf *
>  virtqueue_detatch_unused(struct virtqueue *vq)
>  {
> +	struct virtio_hw *hw = vq->hw;
>  	struct rte_mbuf *cookie;
>  	int idx;
> +	int type = virtio_get_queue_type(hw, vq->vq_queue_index);
> +
> +	if (vq == NULL)
> +		return NULL;
>  
> -	if (vq != NULL)
> -		for (idx = 0; idx < vq->vq_nentries; idx++) {
> +	for (idx = 0; idx < vq->vq_nentries; idx++) {
> +		if (hw->use_simple_rx && type == VTNET_RQ) {
> +			cookie = vq->sw_ring[idx];
> +			if (cookie != NULL) {
> +				vq->sw_ring[idx] = NULL;

Thanks for working on this!

The vq->sw_ring[idx] isn't zeroed during Rx. So besides the
check of (cookie != NULL), some other check is also needed
to avoid freeing the mbufs already delivered to application.

The mbufs in below interval belong to application:

start: sw_ring[vq->vq_avail_idx & (vq->vq_nentries - 1)] (included)
end: sw_ring[(vq->vq_avail_idx + vq->vq_free_cnt) & (vq->vq_nentries - 1)] (excluded)

PS. (vq->vq_avail_idx & (vq->vq_nentries - 1)) can be greater than
    (vq->vq_avail_idx + vq->vq_free_cnt) & (vq->vq_nentries - 1).

Thanks,
Tiwei