reuse the packets after tx burst

[Lokesh Chakka]

Hi Stephen,

Thank you for the information.
It solved your problem.

Regards.
Lokesh.


On Wed, 14 Aug, 2024, 20:29 Stephen Hemminger, <stephen at networkplumber.org>
wrote:

> On Wed, 14 Aug 2024 17:57:40 +0530
> Lokesh Chakka <lvenkatakumarchakka at gmail.com> wrote:
>
> > hi stephen,
> >
> > Thanks for your response. However it seems the solution is not working.
> The
> > following is the modified snippet....
> >
> > while( condition )
> > {
> >      for( pkt_count=0; pkt_count<num_of_pkts_per_queue; pkt_count++ )
> >      {
> >           rte_mbuf_refcnt_set( mbuf[pkt_count], 2 );// setting to two -
> > first and second iteration
> >      }
> >      for( pkt_count=0; pkt_count<5; pkt_count++ )
> >      {
> >           fprintf( stderr, "%s %d %u\n", __func__, __LINE__,
> > rte_mbuf_refcnt_read( mbuf[pkt_count] ) );//able to print two- first and
> > second iteration
> >      }
> >      if( rte_eth_tx_burst( port_id, 0, mbuf, num_of_pkts_per_queue ) !=
> > num_of_pkts_per_queue )
> >      {
> >           fprintf( stderr, "%s %d %d %s\n", __func__, __LINE__,
> rte_errno,
> > rte_strerror(rte_errno) );//failing second time
> >           rte_exit( EXIT_FAILURE, "%s %d rte_eth_tx_burst port id: %u\n",
> > __func__, __LINE__, port_id );
> >      }
> >      fprintf( stderr, "%s %d port: %u sent %u packets\n", __func__,
> > __LINE__, port_id, num_of_pkts_per_queue );//able to send once - first
> > iteration only
> >      for( pkt_count=0; pkt_count<5; pkt_count++ )
> >      {
> >           fprintf( stderr, "%s %d %u\n", __func__, __LINE__,
> > rte_mbuf_refcnt_read( mbuf[pkt_count] ) );//refcnt is printing one
> >      }
> > }
> >
> > There seems to be some more gap in my understanding. Could you please
> help
> > understand the issue?
> >
> > Thanks & Regards
> > --
> > Lokesh Chakka.
> >
> >
> > On Mon, Aug 12, 2024 at 8:22 PM Stephen Hemminger <
> > stephen at networkplumber.org> wrote:
> >
> > > On Mon, 12 Aug 2024 15:55:50 +0530
> > > Lokesh Chakka <lvenkatakumarchakka at gmail.com> wrote:
> > >
> > > > hello,
> > > >
> > > > Here is a small piece of code :
> > > >
> > > > while( condition )
> > > > {
> > > >
> > > >       if( rte_eth_tx_burst( port_id, 0, mbuf, num_of_pkts_per_queue
> ) !=
> > > > num_of_pkts_per_queue )
> > > >       {
> > > >               fprintf( stderr, "%d %s\n", rte_errno,
> > > rte_strerror(rte_errno) );
> > > >               rte_exit( EXIT_FAILURE, "%s %d rte_eth_tx_burst port
> id:
> > > %u\n",
> > > > __func__, __LINE__, port_id );//second iteration failing.
> > > >       }
> > > >       fprintf( stderr, "%s %d port: %u packet: %c sent %u packets\n",
> > > > __func__, __LINE__, port_id, argv[3][0], num_of_pkts_per_queue
> > > > );//printing once
> > > >       for( pkt_count=0; pkt_count<num_of_pkts_per_queue; pkt_count++
> )
> > > >       {//want to send same data again...!!!
> > > >               mbuf[pkt_count]->pkt_len = mbuf[pkt_count]->data_len
> =
> > > dev_info.max_mtu;
> > > >
> > > >       }
> > > >
> > > > }
> > > >
> > > > Can someone help me understand how to reuse the packets again to
> send the
> > > > same data ?
> > > >
> > >
> > > When packet is passed to tx_burst, the ownership of that mbuf is passed
> > > to the driver. The driver will free it after it is sent.
> > >
> > > One option would be to increase the reference count on the packet
> before
> > > sending.
> > > Using rte_mbuf_refcnt_update() function to add one to refcount.
> > > Then the driver will decrement refcount and the refcount will still be
> one
> > > (not freed).
> > >
> > > Assume this is some kind of packet generator.
> > >
>
>
> Don't use refcnt_set(), you want to add an additional refcount not force
> it to two.
> The device driver may hold onto the mbuf for a while after it was passed
> to tx_burst
> so can't assume a value of two.
>
> If the number actually queued is less that the number requested, that
> means the device
> transmit queue is now full. Need to handle that case.
>
> Something like this might get you started:
>
>
> volatile running = true;
>
> void flood(uint16_t port_id, struct rte_mbufs *mbufs[], uint16_t num_pkts)
> {
>
>         while (running) {
>                 /* Add additional reference to retain the packets */
>                 for (uint16_t i = 0; i < num_pkts; i++)
>                         rte_mbuf_refcnt_update(mbufs[i], 1);
>
>                 uint16_t sent = rte_eth_tx_burst(port_id, queue_id, mbufs,
> num_pkts);
>
>                 if (sent < num_pkts) {
>                         /* device transmit queue was full, drop our
> reference */
>                         for (uint16_t i = sent; i < num_pkts; i++)
>                                 rte_pktmbuf_free(mbufs[i]);
>                 }
>         }
>
>         /* Don't leak original version */
>         rte_pktmbuf_free_bulk(mbufs, num_pkts);
>
> }
>
>
>
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