> -----Original Message-----
> From: Xie, Huawei
> Sent: Sunday, May 31, 2015 5:11 PM
> To: Ouyang, Changchun; dev at dpdk.org
> Cc: Cao, Waterman
> Subject: Re: [PATCH v2 5/5] lib_vhost: Add support copying scattered mbuf
> to vring
>
> virtio_dev_rx & scatter_rx & merge-able rx should be merged and the code
> could be much simpler, unless there is special performance consideration.
>
Then, any specific suggestion on how to merge them?
I do consider the performance influence here, so I think it deserve to have 3
implementation for different cases.
>
> On 5/28/2015 11:17 PM, Ouyang, Changchun wrote:
> > Add support copying scattered mbuf to vring which is done by
> > dev_scatter_rx, and check the 'next' pointer in mbuf on the fly to select
> suitable function to rx packets.
> >
> > Signed-off-by: Changchun Ouyang <changchun.ouyang at intel.com>
> > ---
> > lib/librte_vhost/vhost_rxtx.c | 116
> > +++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 115 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/librte_vhost/vhost_rxtx.c
> > b/lib/librte_vhost/vhost_rxtx.c index bb56ae1..3086bb4 100644
> > --- a/lib/librte_vhost/vhost_rxtx.c
> > +++ b/lib/librte_vhost/vhost_rxtx.c
> > @@ -46,7 +46,8 @@
> > * This function adds buffers to the virtio devices RX virtqueue. Buffers
> > can
> > * be received from the physical port or from another virtio device. A
> packet
> > * count is returned to indicate the number of packets that are
> > succesfully
> > - * added to the RX queue. This function works when mergeable is disabled.
> > + * added to the RX queue. This function works when mergeable is
> > + disabled and
> > + * the mbuf is not scattered.
> > */
> > static inline uint32_t __attribute__((always_inline))
> > virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id, @@ -447,6
> > +448,103 @@ fill_buf_vec(struct vhost_virtqueue *vq, uint16_t id,
> > uint32_t *vec_idx) }
> >
> > /*
> > + * This function works for scatter-gather RX.
> > + */
> > +static inline uint32_t __attribute__((always_inline))
> > +virtio_dev_scatter_rx(struct virtio_net *dev, uint16_t queue_id,
> > + struct rte_mbuf **pkts, uint32_t count) {
> > + struct vhost_virtqueue *vq;
> > + uint32_t pkt_idx = 0, entry_success = 0;
> > + uint16_t avail_idx;
> > + uint16_t res_base_idx, res_end_idx;
> > + uint8_t success = 0;
> > +
> > + LOG_DEBUG(VHOST_DATA, "(%"PRIu64") virtio_dev_scatter_rx()\n",
> > + dev->device_fh);
> use __func__
> > + if (unlikely(queue_id != VIRTIO_RXQ))
> > + LOG_DEBUG(VHOST_DATA, "mq isn't supported in this
> version.\n");
> > +
> > + vq = dev->virtqueue[VIRTIO_RXQ];
> > + count = RTE_MIN((uint32_t)MAX_PKT_BURST, count);
> > +
> > + if (count == 0)
> > + return 0;
> > +
> > + for (pkt_idx = 0; pkt_idx < count; pkt_idx++) {
> > + uint32_t secure_len = 0;
> > + uint32_t vec_idx = 0;
> > + uint32_t pkt_len = pkts[pkt_idx]->pkt_len + vq->vhost_hlen;
> > +
> > + do {
> > + /*
> > + * As many data cores may want access to available
> > + * buffers, they need to be reserved.
> > + */
> > + res_base_idx = vq->last_used_idx_res;
> > + avail_idx = *((volatile uint16_t *)&vq->avail->idx);
> > +
> > + if (unlikely(res_base_idx == avail_idx)) {
> > + LOG_DEBUG(VHOST_DATA,
> > + "(%"PRIu64") Failed "
> > + "to get enough desc from "
> > + "vring\n",
> > + dev->device_fh);
> > + return pkt_idx;
> > + } else {
> > + uint16_t wrapped_idx =
> > + (res_base_idx) & (vq->size - 1);
> > + uint32_t idx = vq->avail->ring[wrapped_idx];
> > +
> > + update_secure_len(vq, idx, &secure_len);
> > + }
> > +
> > + if (pkt_len > secure_len) {
> > + LOG_DEBUG(VHOST_DATA,
> > + "(%"PRIu64") Failed "
> > + "to get enough desc from "
> > + "vring\n",
> > + dev->device_fh);
> > + return pkt_idx;
> > + }
> The behavior for virtio_dev_rx and virtio_dev_merge_rx is totally different. I
> think they should behave in the same way.
Why they have to work as same way?
> virtio_dev_rx updates used->len to zero while this one returns immediately.
>
Yes, if it is uncompleted packets, I think it comes from your comments about
dropping the packets if the room is not
Big enough to contain the whole packet.
> Besides, with this implementation, if the caller retransmit the mbuf(which
> has pkt_len larger the secure_len), it will enter endless loop.
Why the caller retransmit the mbuf? I think this is caller's bad, then endless
loop just catch that issue in caller.
>
> > +
> > + /* vq->last_used_idx_res is atomically updated. */
> > + success = rte_atomic16_cmpset(&vq-
> >last_used_idx_res,
> > + res_base_idx,
> > + res_base_idx + 1);
> > + } while (success == 0);
>
> Here the behavior becomes different again in reserving vring entries.
>
> > +
> > + fill_buf_vec(vq, res_base_idx, &vec_idx);
> > +
> > + res_end_idx = res_base_idx + 1;
> > +
> > + entry_success = copy_from_mbuf_to_vring(dev,
> res_base_idx,
> > + res_end_idx, pkts[pkt_idx]);
> > +
> > + rte_compiler_barrier();
> > +
> > + /*
> > + * Wait until it's our turn to add our buffer
> > + * to the used ring.
> > + */
> > + while (unlikely(vq->last_used_idx != res_base_idx))
> > + rte_pause();
> > +
> > + *(volatile uint16_t *)&vq->used->idx += entry_success;
> > + vq->last_used_idx = res_end_idx;
> > +
> > + /* flush used->idx update before we read avail->flags. */
> > + rte_mb();
> > +
> > + /* Kick the guest if necessary. */
> > + if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT))
> > + eventfd_write((int)vq->callfd, 1);
> > + }
> > +
> > + return count;
> > +}
> > +
> > +/*
> > * This function works for mergeable RX.
> > */
> > static inline uint32_t __attribute__((always_inline)) @@ -545,12
> > +643,28 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t
> queue_id,
> > return count;
> > }
> >
> > +/*
> > + * Return 1 if any mbuf is scattered, otherwise return 0.
> > + */
> > +static inline uint32_t __attribute__((always_inline))
> > +check_scatter(struct rte_mbuf **pkts, uint16_t count) {
> > + uint32_t i;
> > + for (i = 0; i < count; i++) {
> > + if (pkts[i]->next != NULL)
> > + return 1;
> > + }
> > + return 0;
> > +}
> > +
> > uint16_t
> > rte_vhost_enqueue_burst(struct virtio_net *dev, uint16_t queue_id,
> > struct rte_mbuf **pkts, uint16_t count) {
> > if (unlikely(dev->features & (1 << VIRTIO_NET_F_MRG_RXBUF)))
> > return virtio_dev_merge_rx(dev, queue_id, pkts, count);
> > + else if (unlikely(check_scatter(pkts, count) == 1))
> > + return virtio_dev_scatter_rx(dev, queue_id, pkts, count);
> > else
> > return virtio_dev_rx(dev, queue_id, pkts, count); }
