[dpdk-dev] [PATCH v5 1/4] vhost: abstract and reorganize async split ring code

[Jiang, Cheng1]

Hi Jiayu,

> -----Original Message-----
> From: Hu, Jiayu <jiayu.hu at intel.com>
> Sent: Tuesday, April 13, 2021 10:44 AM
> To: Jiang, Cheng1 <cheng1.jiang at intel.com>; maxime.coquelin at redhat.com;
> Xia, Chenbo <chenbo.xia at intel.com>
> Cc: dev at dpdk.org; Yang, YvonneX <yvonnex.yang at intel.com>; Wang, Yinan
> <yinan.wang at intel.com>; Liu, Yong <yong.liu at intel.com>
> Subject: RE: [PATCH v5 1/4] vhost: abstract and reorganize async split ring
> code
> 
> Hi Cheng,
> 
> Some comments inline.
> 
> > -----Original Message-----
> > From: Jiang, Cheng1 <cheng1.jiang at intel.com>
> > Sent: Monday, April 12, 2021 7:34 PM
> > To: maxime.coquelin at redhat.com; Xia, Chenbo <chenbo.xia at intel.com>
> > Cc: dev at dpdk.org; Hu, Jiayu <jiayu.hu at intel.com>; Yang, YvonneX
> > <yvonnex.yang at intel.com>; Wang, Yinan <yinan.wang at intel.com>; Liu,
> > Yong <yong.liu at intel.com>; Jiang, Cheng1 <cheng1.jiang at intel.com>
> > Subject: [PATCH v5 1/4] vhost: abstract and reorganize async split
> > ring code
> >
> > In order to improve code efficiency and readability when async packed
> > ring support is enabled. This patch abstract some functions like
> > shadow_ring_store and write_back_completed_descs_split. And improve
> > the efficiency of some pointer offset calculation.
> 
> Need to improve grammar for commit log, as there is typo and incomplete
> sentence.
> 

Sure, I'll fix it in the next version.

> >
> > Signed-off-by: Cheng Jiang <Cheng1.jiang at intel.com>
> > ---
> >  lib/librte_vhost/virtio_net.c | 146
> > +++++++++++++++++++---------------
> >  1 file changed, 84 insertions(+), 62 deletions(-)
> >
> > diff --git a/lib/librte_vhost/virtio_net.c
> > b/lib/librte_vhost/virtio_net.c index ff3987860..c43ab0093 100644
> > --- a/lib/librte_vhost/virtio_net.c
> > +++ b/lib/librte_vhost/virtio_net.c
> > @@ -1458,6 +1458,29 @@ virtio_dev_rx_async_get_info_idx(uint16_t
> > pkts_idx,
> >  (vq_size - n_inflight + pkts_idx) & (vq_size - 1);  }
> >
> > +static __rte_always_inline void
> > +shadow_ring_store(struct vhost_virtqueue *vq,  void *shadow_ring,
> > +void
> > *d_ring,
> > +uint16_t s_idx, uint16_t d_idx,
> > +uint16_t count, uint16_t elem_size)
> > +{
> > +if (d_idx + count <= vq->size) {
> > +rte_memcpy((void *)((uintptr_t)d_ring + d_idx * elem_size), (void
> > +*)((uintptr_t)shadow_ring + s_idx * elem_size), count * elem_size); }
> > +else { uint16_t size = vq->size - d_idx;
> > +
> > +rte_memcpy((void *)((uintptr_t)d_ring + d_idx * elem_size), (void
> > +*)((uintptr_t)shadow_ring + s_idx * elem_size), size * elem_size);
> > +
> > +rte_memcpy((void *)((uintptr_t)d_ring), (void
> > +*)((uintptr_t)shadow_ring + (s_idx + size) * elem_size), (count -
> > +size) * elem_size); } }
> > +
> >  static __rte_noinline uint32_t
> >  virtio_dev_rx_async_submit_split(struct virtio_net *dev,  struct
> > vhost_virtqueue *vq, uint16_t queue_id, @@ -1478,6 +1501,7 @@
> > virtio_dev_rx_async_submit_split(struct virtio_net *dev,  struct
> > rte_vhost_iov_iter *dst_it = it_pool + 1;  uint16_t slot_idx = 0;
> > uint16_t segs_await = 0;
> > +uint16_t iovec_idx = 0, it_idx = 0;
> >  struct async_inflight_info *pkts_info = vq->async_pkts_info;
> > uint32_t n_pkts = 0, pkt_err = 0;  uint32_t num_async_pkts = 0,
> > num_done_pkts = 0; @@ -1513,27 +1537,32 @@
> > virtio_dev_rx_async_submit_split(struct
> > virtio_net *dev,
> >
> >  if (async_mbuf_to_desc(dev, vq, pkts[pkt_idx],  buf_vec, nr_vec,
> > num_buffers, -src_iovec, dst_iovec, src_it, dst_it) < 0) {
> > +&src_iovec[iovec_idx],
> > +&dst_iovec[iovec_idx],
> > +&src_it[it_idx],
> > +&dst_it[it_idx]) < 0) {
> 
> When use index, it's strange to get src and dst iov_iter from dst_it and src_it
> respectively, as they are not start addresses of two separated iov_iter arrays
> but have overlapped elements. IMO, there is no need to use src/dst_it, as
> they can be simply indexed by it_pool[it_idx] and it_pool[it_idx+1].

Yes, I think it make sense, I'll fix it in the next version.

> 
> >  vq->shadow_used_idx -= num_buffers;
> >  break;
> >  }
> >
> >  slot_idx = (vq->async_pkts_idx + num_async_pkts) &  (vq->size - 1);
> > -if (src_it->count) {
> > +if (src_it[it_idx].count) {
> >  uint16_t from, to;
> >
> > -async_fill_desc(&tdes[pkt_burst_idx++], src_it, dst_it);
> > +async_fill_desc(&tdes[pkt_burst_idx++],
> > +&src_it[it_idx],
> > +&dst_it[it_idx]);
> >  pkts_info[slot_idx].descs = num_buffers;  pkts_info[slot_idx].mbuf =
> > pkts[pkt_idx];  async_pkts_log[num_async_pkts].pkt_idx = pkt_idx;
> > async_pkts_log[num_async_pkts++].last_avail_idx =  vq->last_avail_idx;
> > -src_iovec += src_it->nr_segs; -dst_iovec += dst_it->nr_segs; -src_it
> > += 2; -dst_it += 2; -segs_await += src_it->nr_segs;
> > +
> > +iovec_idx += src_it[it_idx].nr_segs;
> > +it_idx += 2;
> > +
> > +segs_await += src_it[it_idx].nr_segs;
> >
> >  /**
> >   * recover shadow used ring and keep DMA-occupied @@ -1541,23
> > +1570,12 @@ virtio_dev_rx_async_submit_split(struct
> > virtio_net *dev,
> >   */
> >  from = vq->shadow_used_idx - num_buffers;  to = vq->async_desc_idx &
> > (vq->size - 1); -if (num_buffers + to <= vq->size) {
> > -rte_memcpy(&vq->async_descs_split[to],
> > -&vq-
> > >shadow_used_split[from],
> > -num_buffers *
> > -sizeof(struct
> > vring_used_elem));
> > -} else {
> > -int size = vq->size - to;
> > -
> > -rte_memcpy(&vq->async_descs_split[to],
> > -&vq-
> > >shadow_used_split[from],
> > -size *
> > -sizeof(struct
> > vring_used_elem));
> > -rte_memcpy(vq->async_descs_split,
> > -&vq-
> > >shadow_used_split[from +
> > -size], (num_buffers - size) *
> > -   sizeof(struct vring_used_elem));
> > -}
> > +
> > +shadow_ring_store(vq, vq->shadow_used_split,
> > +vq->async_descs_split,
> > +from, to, num_buffers,
> > +sizeof(struct vring_used_elem));
> 
> This function is to store DMA-occupied desc, but " shadow_ring_store" is not
> a good name for it. In addition, I think there is no need to pass vq as a
> parameter. What you need is the size of shadow ring and async desc ring.

Ok, I think we can use the name " store_dma_desc_info()".

Thanks a lot.
Cheng

> 
> Thanks,
> Jiayu
> > +
> >  vq->async_desc_idx += num_buffers;
> >  vq->shadow_used_idx -= num_buffers;
> >  } else
> > @@ -1575,10 +1593,9 @@ virtio_dev_rx_async_submit_split(struct
> > virtio_net *dev,
> >  BUF_VECTOR_MAX))) {
> >  n_pkts = vq->async_ops.transfer_data(dev->vid,
> >  queue_id, tdes, 0, pkt_burst_idx);
> > -src_iovec = vec_pool;
> > -dst_iovec = vec_pool + (VHOST_MAX_ASYNC_VEC >> 1); -src_it = it_pool;
> > -dst_it = it_pool + 1;
> > +iovec_idx = 0;
> > +it_idx = 0;
> > +
> >  segs_await = 0;
> >  vq->async_pkts_inflight_n += n_pkts;
> >
> > @@ -1639,6 +1656,43 @@ virtio_dev_rx_async_submit_split(struct
> > virtio_net *dev,
> >  return pkt_idx;
> >  }
> >
> > +static __rte_always_inline void
> > +write_back_completed_descs_split(struct vhost_virtqueue *vq, uint16_t
> > n_descs)
> > +{
> > +uint16_t nr_left = n_descs;
> > +uint16_t nr_copy;
> > +uint16_t to, from;
> > +
> > +do {
> > +from = vq->last_async_desc_idx & (vq->size - 1); nr_copy = nr_left +
> > +from <= vq->size ? nr_left :
> > +vq->size - from;
> > +to = vq->last_used_idx & (vq->size - 1);
> > +
> > +if (to + nr_copy <= vq->size) {
> > +rte_memcpy(&vq->used->ring[to],
> > +&vq->async_descs_split[from],
> > +nr_copy *
> > +sizeof(struct vring_used_elem));
> > +} else {
> > +uint16_t size = vq->size - to;
> > +
> > +rte_memcpy(&vq->used->ring[to],
> > +&vq->async_descs_split[from],
> > +size *
> > +sizeof(struct vring_used_elem));
> > +rte_memcpy(vq->used->ring,
> > +&vq->async_descs_split[from +
> > +size], (nr_copy - size) *
> > +sizeof(struct vring_used_elem));
> > +}
> > +
> > +vq->last_async_desc_idx += nr_copy;
> > +vq->last_used_idx += nr_copy;
> > +nr_left -= nr_copy;
> > +} while (nr_left > 0);
> > +}
> > +
> >  uint16_t rte_vhost_poll_enqueue_completed(int vid, uint16_t queue_id,
> > struct rte_mbuf **pkts, uint16_t count)  { @@ -1695,39 +1749,7 @@
> > uint16_t rte_vhost_poll_enqueue_completed(int
> > vid, uint16_t queue_id,
> >  vq->async_pkts_inflight_n -= n_pkts_put;
> >
> >  if (likely(vq->enabled && vq->access_ok)) { -uint16_t nr_left =
> > n_descs; -uint16_t nr_copy; -uint16_t to;
> > -
> > -/* write back completed descriptors to used ring */ -do { -from =
> > vq->last_async_desc_idx & (vq->size - 1); -nr_copy = nr_left + from <=
> > vq->size ? nr_left :
> > -vq->size - from;
> > -to = vq->last_used_idx & (vq->size - 1);
> > -
> > -if (to + nr_copy <= vq->size) {
> > -rte_memcpy(&vq->used->ring[to],
> > -&vq-
> > >async_descs_split[from],
> > -nr_copy *
> > -sizeof(struct
> > vring_used_elem));
> > -} else {
> > -uint16_t size = vq->size - to;
> > -
> > -rte_memcpy(&vq->used->ring[to],
> > -&vq-
> > >async_descs_split[from],
> > -size *
> > -sizeof(struct
> > vring_used_elem));
> > -rte_memcpy(vq->used->ring,
> > -&vq->async_descs_split[from
> > +
> > -size], (nr_copy - size) *
> > -sizeof(struct
> > vring_used_elem));
> > -}
> > -
> > -vq->last_async_desc_idx += nr_copy;
> > -vq->last_used_idx += nr_copy;
> > -nr_left -= nr_copy;
> > -} while (nr_left > 0);
> > +write_back_completed_descs_split(vq, n_descs);
> >
> >  __atomic_add_fetch(&vq->used->idx, n_descs, __ATOMIC_RELEASE);
> > vhost_vring_call_split(dev, vq);
> > --
> > 2.29.2
>