Re: [PATCH] app: fix silent enqueue fail in test_mbuf test_refcnt_iter

[Olivier Matz <olivier.matz@6wind.com>]

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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