Re: [PATCH v2 4/4] vhost: improve RARP handling in dequeue paths

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 1/15/25 5:46 PM, David Marchand wrote:
> On Wed, Jan 15, 2025 at 1:59 PM Maxime Coquelin
> <maxime.coquelin@redhat.com> wrote:
>>
>> With previous refactoring, we can now simplify the RARP
>> packet injection handling in both the sync and async
>> dequeue paths.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>   lib/vhost/virtio_net.c | 42 ++++++++++++++++++------------------------
>>   1 file changed, 18 insertions(+), 24 deletions(-)
>>
>> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
>> index 59ea2d16a5..fab45ebd54 100644
>> --- a/lib/vhost/virtio_net.c
>> +++ b/lib/vhost/virtio_net.c
>> @@ -3662,21 +3662,23 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
>>                   * learning table will get updated first.
>>                   */
>>                  pkts[0] = rarp_mbuf;
> 
> Well, ideally it would be pkts[nb_rx], but see comment below.
> 
>> -               vhost_queue_stats_update(dev, vq, pkts, 1);
>> -               pkts++;
>> -               count -= 1;
>> +               nb_rx += 1;
>>          }
> 
> With this change, the rarp_mbuf variable is unneeded.
> You can store to pkts[nb_rx] when calling rte_net_make_rarp_packet()
> (and at the same time, move the comment about injecting the packet to
> the head of the array).

I agree with this further simplification.

Thanks,
Maxime

> 
> 
> 
>>
>>          if (vq_is_packed(dev)) {
>>                  if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
>> -                       nb_rx = virtio_dev_tx_packed_legacy(dev, vq, mbuf_pool, pkts, count);
>> +                       nb_rx += virtio_dev_tx_packed_legacy(dev, vq, mbuf_pool,
>> +                                       pkts + nb_rx, count - nb_rx);
>>                  else
>> -                       nb_rx = virtio_dev_tx_packed_compliant(dev, vq, mbuf_pool, pkts, count);
>> +                       nb_rx += virtio_dev_tx_packed_compliant(dev, vq, mbuf_pool,
>> +                                       pkts + nb_rx, count - nb_rx);
>>          } else {
>>                  if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
>> -                       nb_rx = virtio_dev_tx_split_legacy(dev, vq, mbuf_pool, pkts, count);
>> +                       nb_rx += virtio_dev_tx_split_legacy(dev, vq, mbuf_pool,
>> +                                       pkts + nb_rx, count - nb_rx);
>>                  else
>> -                       nb_rx = virtio_dev_tx_split_compliant(dev, vq, mbuf_pool, pkts, count);
>> +                       nb_rx += virtio_dev_tx_split_compliant(dev, vq, mbuf_pool,
>> +                                       pkts + nb_rx, count - nb_rx);
>>          }
>>
>>          vhost_queue_stats_update(dev, vq, pkts, nb_rx);
>> @@ -3687,9 +3689,6 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
>>   out_access_unlock:
>>          rte_rwlock_read_unlock(&vq->access_lock);
>>
>> -       if (unlikely(rarp_mbuf != NULL))
>> -               nb_rx += 1;
>> -
>>   out_no_unlock:
>>          return nb_rx;
>>   }
>> @@ -4285,25 +4284,23 @@ rte_vhost_async_try_dequeue_burst(int vid, uint16_t queue_id,
>>                   * learning table will get updated first.
>>                   */
>>                  pkts[0] = rarp_mbuf;
>> -               vhost_queue_stats_update(dev, vq, pkts, 1);
>> -               pkts++;
>> -               count -= 1;
>> +               nb_rx += 1;
>>          }
> 
> Idem.
> 
>>
>>          if (vq_is_packed(dev)) {
>>                  if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
>> -                       nb_rx = virtio_dev_tx_async_packed_legacy(dev, vq, mbuf_pool,
>> -                                       pkts, count, dma_id, vchan_id);
>> +                       nb_rx += virtio_dev_tx_async_packed_legacy(dev, vq, mbuf_pool,
>> +                                       pkts + nb_rx, count - nb_rx, dma_id, vchan_id);
>>                  else
>> -                       nb_rx = virtio_dev_tx_async_packed_compliant(dev, vq, mbuf_pool,
>> -                                       pkts, count, dma_id, vchan_id);
>> +                       nb_rx += virtio_dev_tx_async_packed_compliant(dev, vq, mbuf_pool,
>> +                                       pkts + nb_rx, count - nb_rx, dma_id, vchan_id);
>>          } else {
>>                  if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
>> -                       nb_rx = virtio_dev_tx_async_split_legacy(dev, vq, mbuf_pool,
>> -                                       pkts, count, dma_id, vchan_id);
>> +                       nb_rx += virtio_dev_tx_async_split_legacy(dev, vq, mbuf_pool,
>> +                                       pkts + nb_rx, count - nb_rx, dma_id, vchan_id);
>>                  else
>> -                       nb_rx = virtio_dev_tx_async_split_compliant(dev, vq, mbuf_pool,
>> -                                       pkts, count, dma_id, vchan_id);
>> +                       nb_rx += virtio_dev_tx_async_split_compliant(dev, vq, mbuf_pool,
>> +                                       pkts + nb_rx, count - nb_rx, dma_id, vchan_id);
>>          }
>>
>>          *nr_inflight = vq->async->pkts_inflight_n;
>> @@ -4315,9 +4312,6 @@ rte_vhost_async_try_dequeue_burst(int vid, uint16_t queue_id,
>>   out_access_unlock:
>>          rte_rwlock_read_unlock(&vq->access_lock);
>>
>> -       if (unlikely(rarp_mbuf != NULL))
>> -               nb_rx += 1;
>> -
>>   out_no_unlock:
>>          return nb_rx;
>>   }
>> --
>> 2.47.1
>>
> 
>