rte_eth_rx_burst only returns up to 32 packets

Hi,

The documentation of this method says: Applications implementing a "retrieve as much received packets as possible" policy can check this specific case and keep invoking the rte_eth_rx_burst() <http://dpdk.org/doc/api/rte__ethdev_8h.html#aee7daffe261e67355a78b106627c4c45>function until a value less than nb_pkts is returned.

But the function returns at most 32 packets regardless of the burst size parameter (nb_pkts). For example when I set the burst size to 256, it only returns 32 packets even though the queue has more packets. This means that I cannot rely on the returned value to know if there are > 256 packets in the queue or not.

Where this number 32 comes from? Is it because "PMD: ixgbe_set_rx_function(): Vector rx enabled, please make sure RX burst size no less than 32." ?

I use DPDK 2.0.0 and Intel 82599 10 G NIC.

Thanks

Please see _rece_raw_pkts_vec function.

Here is part of its comments may explain this question
/*
* vPMD receive routine, now only accept (nb_pkts == RTE_IXGBE_VPMD_RX_BURST)
* in one loop
*
* Notice:
* - nb_pkts < RTE_IXGBE_VPMD_RX_BURST, just return no packet
* - nb_pkts > RTE_IXGBE_VPMD_RX_BURST, only scan RTE_IXGBE_VPMD_RX_BURST
* numbers of DD bit
*/

Hi,

The documentation of this method says: Applications implementing a "retrieve as much received packets as possible" policy can check this specific case and keep invoking the rte_eth_rx_burst() <http://dpdk.org/doc/api/rte__ethdev_8h.html#aee7daffe261e67355a78b106627c4c45>function
until a value less than nb_pkts is returned.

But the function returns at most 32 packets regardless of the burst size parameter (nb_pkts). For example when I set the burst size to 256, it only returns 32 packets even though the queue has more packets. This means that I cannot rely on the returned value to know if there are > 256 packets in the queue or not.

Where this number 32 comes from? Is it because "PMD:
ixgbe_set_rx_function(): Vector rx enabled, please make sure RX burst size no less than 32." ?

I use DPDK 2.0.0 and Intel 82599 10 G NIC.

Thanks

Thanks a lot.

So I assume the only way to see if there are more than 256 packets in the queue is to count them using rte_eth_rx_count

Sorry for bulging in but i think Masood rose a very important general question here, which is: how do i check if there are more pending packets in the PMD Rx queue without actually polling them (out)?

As far as i see it the short answer is you can't. Or more specifically - you shouldn't. Because if it happens that your code depends on it - it most likely doesn't fit the PMD model.

The thing is that u can actually go and query the Rx ring about the number of pending packets but the truth is that by the time u get this query result it may already be wrong since new packets have arrived.

The only correct way to deal with PMD Rx queue is to actually go and poll for new packets: if there are some - handle them and if there aren't any - poll again.

This is my understanding of this.

Thanks,
Vlad

RTE_IXGBE_VPMD_RX_BURST

http://dpdk.org/doc/api/rte__ethdev_8h.html#aee7daffe261e67355a78b106627c4c45

only

that

size