[dpdk-users] Packets drop while fetching with rte_eth_rx_burst

Filip Janiszewski contact at filipjaniszewski.com
Sun Mar 25 12:33:09 CEST 2018

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 ) {
    num_of_pkt = rte_eth_rx_burst( config->port_id,
    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 =
        //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.


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