[dpdk-users] 回覆﹕ Packets drop while fetching with rte_eth_rx_burst

[Filip Janiszewski]

Thanks Marco,

I'm running DPDK 18.02. I might understand that the counter is not
implemented yet, but why rte_eth_rx_burst never returns nb_pkts?
According to:
http://dpdk.org/doc/api/rte__ethdev_8h.html#a3e7d76a451b46348686ea97d6367f102

"The rte_eth_rx_burst() function returns the number of packets actually
retrieved, which is the number of rte_mbuf data structures effectively
supplied into the rx_pkts array. A return value equal to nb_pkts
indicates that the RX queue contained at least rx_pkts packets, and this
is likely to signify that other received packets remain in the input queue."

So in case of drops I would expect the rx queue to be full and
rte_eth_rx_burst to return nb_pkts, but this never happen and it seems
that there's plenty of space in the ring, is that correct?

Thanks

Il 03/25/2018 01:30 PM, MAC Lee ha scritto:
> Hi Filip,
>     which dpdk version are you using? You can take a look to the source code of dpdk , the rxdrop counter may be not implemented in dpdk. So you always get 0 in rxdrop. 
> 
> Thanks,
> Marco
> --------------------------------------------
> 18/3/25 (週日)，Filip Janiszewski <contact at filipjaniszewski.com> 寫道：
> 
>  主旨: [dpdk-users] Packets drop while fetching with rte_eth_rx_burst
>  收件者: users at dpdk.org
>  日期: 2018年3月25日,日,下午6:33
>  
>  Hi Everybody,
>  
>  I have a weird drop problem, and to
>  understand my question the best way
>  is to have a look at this simple (and
>  cleaned from all the not relevant
>  stuff) snippet:
>  
>  while( 1 )
>  {
>      if( config->running ==
>  false ) {
>          break;
>      }
>      num_of_pkt =
>  rte_eth_rx_burst( config->port_id,
>           
>                 
>           config->queue_idx,
>           
>                 
>           buffers,
>           
>                 
>           MAX_BURST_DEQ_SIZE);
>      if( unlikely( num_of_pkt
>  == MAX_BURST_DEQ_SIZE ) ) {
>         
>  rx_ring_full = true; //probably not the best name
>      }
>  
>      if( likely( num_of_pkt
>  > 0 ) )
>      {
>          pk_captured
>  += num_of_pkt;
>  
>         
>  num_of_enq_pkt =
>  rte_ring_sp_enqueue_bulk(config->incoming_pkts_ring,
>           
>                 
>                 
>       (void*)buffers,
>           
>                 
>                 
>       num_of_pkt,
>           
>                 
>                 
>       &rx_ring_free_space);
>          //if
>  num_of_enq_pkt == 0 free the mbufs..
>       }
>  }
>  
>  This loop is retrieving packets from
>  the device and pushing them into a
>  queue for further processing by another
>  lcore.
>  
>  When I run a test with a Mellanox card
>  sending 20M (20878300) packets at
>  2.5M p/s the loop seems to miss some
>  packets and pk_captured is always
>  like 19M or similar.
>  
>  rx_ring_full is never true, which means
>  that num_of_pkt is always <
>  MAX_BURST_DEQ_SIZE, so according to the
>  documentation I shall not have
>  drops at HW level. Also, num_of_enq_pkt
>  is never 0 which means that all
>  the packets are enqueued.
>  
>  Now, if from that snipped I remove the
>  rte_ring_sp_enqueue_bulk call
>  (and make sure to release all the
>  mbufs) then pk_captured is always
>  exactly equal to the amount of packets
>  I've send to the NIC.
>  
>  So it seems (but I cant deal with this
>  idea) that
>  rte_ring_sp_enqueue_bulk is somehow too
>  slow and between one call to
>  rte_eth_rx_burst and another some
>  packets are dropped due to full ring
>  on the NIC, but, why num_of_pkt (from
>  rte_eth_rx_burst) is always
>  smaller than MAX_BURST_DEQ_SIZE (much
>  smaller) as if there was always
>  sufficient room for the packets?
>  
>  Is anybody able to help me understand
>  what's happening here?
>  
>  Note, MAX_BURST_DEQ_SIZE is 512.
>  
>  Thanks
>  
> 

-- 
BR, Filip
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