Hello Julien,

On Tue, Aug 22, 2023 at 08:34:53AM +0200, jhascoet wrote:
> From: Julien Hascoet <ju.hascoet@gmail.com>
>
> In case of ring full state, we retry the enqueue
> operation in order to avoid mbuf loss.
>
> Fixes: af75078fece ("first public release")
>
> Signed-off-by: Julien Hascoet <ju.hascoet@gmail.com>
> ---
>  app/test/test_mbuf.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/app/test/test_mbuf.c b/app/test/test_mbuf.c
> index efac01806b..ad18bf6378 100644
> --- a/app/test/test_mbuf.c
> +++ b/app/test/test_mbuf.c
> @@ -1033,12 +1033,21 @@ test_refcnt_iter(unsigned int lcore, unsigned int iter,
>               tref += ref;
>               if ((ref & 1) != 0) {
>                       rte_pktmbuf_refcnt_update(m, ref);
> -                     while (ref-- != 0)
> -                             rte_ring_enqueue(refcnt_mbuf_ring, m);
> +                     while (ref-- != 0) {
> +                             /* retry in case of failure */
> +                             while (rte_ring_enqueue(refcnt_mbuf_ring, m) != 0) {
> +                                     /* let others consume */
> +                                     rte_pause();
> +                             }
> +                     }
>               } else {
>                       while (ref-- != 0) {
>                               rte_pktmbuf_refcnt_update(m, 1);
> -                             rte_ring_enqueue(refcnt_mbuf_ring, m);
> +                             /* retry in case of failure */
> +                             while (rte_ring_enqueue(refcnt_mbuf_ring, m) != 0) {
> +                                     /* let others consume */
> +                                     rte_pause();
> +                             }
>                       }
>               }
>               rte_pktmbuf_free(m);
> --
> 2.34.1
>

Can you give some more details about how to reproduce the issue?

From what I see, the code does the following:

main core:
  create a ring with at least (REFCNT_MBUF_NUM * REFCNT_MAX_REF) entries
  create an mbuf pool with REFCNT_MBUF_NUM entries
  start worker cores
  do REFCNT_MAX_ITER times:
    for each mbuf of the pool (REFCNT_MBUF_NUM entries):
      let r be a random number between 1 and REFCNT_MAX_REF
      increase mbuf references by r, and enqueue r times in the ring
    wait that the ring is empty (since worker cores are dequeuing mbufs)
  stop worker cores

worker cores:
  dequeue packets from the ring and free them until asked to stop


I may be mistaking but I don't see how the number of mbufs in ring could
exceed REFCNT_MBUF_NUM * REFCNT_MAX_REF.

Regards,
Olivier


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