Hi! I am just writing my first code using dpdk, a traffic generator, for which I started with the l2fwd example.
Basically, I need to send the same packet over a single interface, over an over again, with single bytes changed each time. I use rte_eth_tx_burst to send 16 packets at once. As I want to re-use the same buffers in a very simple way, I just increment the refcnt accordingly. My current code prepares all 16 buffers, calls rte_eth_tx_burst until all 16 packets are stored in the transmit ring, and starts over again, adjusting the buffers to send the next 16 packets. Currently I observe duplicate packets, although every packet should be individual due to single byte adjustments. My current problem is, as I guess, that rte_eth_tx_burst does not synchnolously transmit the count of packets, which is returned to the caller, but just stores them in transmit queue. So, I am not allowed to instantly re-use these buffers again. My question is: How do I know when to re-use buffers passed to rte_eth_tx_burst. Of course, I can check their refcnt member, and this would be perfectly fine. Apparently, I should have at least BURST_SIZE*2 buffers, passing BURST_SIZE buffers at once, so I can manipulate one set of buffers while the other is transmitted. But I am missing the idea of the best synchronization scheme here: How should I wait on this refcnt to drop? Some blind guessing: If I take the documentation of rte_eth_tx_burst literally, I could get the idea that refcounts of buffers are only decreased (buffers are 'freed'), while rte_eth_tx_burst is executed, but one function call might free buffers used by previous function calls. If this is correct, I still do not see a complete synchronization scheme. There is still a chance that I end up without any buffers left, which means I do not have a chance to call rte_eth_tx_burst again to free buffers. Thanks for any help, Philipp