Re: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer length

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi,

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Jean-Mickael Guerin
> Sent: Thursday, December 04, 2014 2:26 PM
> To: dev@dpdk.org
> Subject: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer length
> 
> The template mbuf_initializer is hard coded with a buflen which
> might have been set differently by the application at the time of
> mbuf pool creation.
> 
> Switch to a mbuf allocation, to fetch the correct default values.
> There is no performance impact because this is not a data-plane API.
> 
> Signed-off-by: Jean-Mickael Guerin <jean-mickael.guerin@6wind.com>
> Acked-by: David Marchand <david.marchand@6wind.com>
> Fixes: 0ff3324da2 ("ixgbe: rework vector pmd following mbuf changes")
> ---
>  lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> index c1b5a78..f7b02f5 100644
> --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> @@ -732,17 +732,22 @@ static struct ixgbe_txq_ops vec_txq_ops = {
>  int
>  ixgbe_rxq_vec_setup(struct igb_rx_queue *rxq)
>  {
> -	struct rte_mbuf mb_def = { .buf_addr = 0 }; /* zeroed mbuf */
> +	struct rte_mbuf *mb_def;
> 
> -	mb_def.nb_segs = 1;
> -	mb_def.data_off = RTE_PKTMBUF_HEADROOM;
> -	mb_def.buf_len = rxq->mb_pool->elt_size - sizeof(struct rte_mbuf);
> -	mb_def.port = rxq->port_id;
> -	rte_mbuf_refcnt_set(&mb_def, 1);
> +	mb_def = rte_pktmbuf_alloc(rxq->mb_pool);

Could you explain to me, what is an advantage of using dynamic allocation vs local struct here?
I don't see any.
Plus if rte_pktmbuf_alloc() would fail, we'll leave our rx queue not configured properly.
As I can see ixgbe_dev_rx_queue_setup() doesn't check the return value of >  ixgbe_rxq_vec_setup()
(as it is just not supposed to fail).
So ixgbe_dev_rx_queue_setup() will return OK for unconfigured RX queue.

> +	if (mb_def == NULL) {
> +		PMD_INIT_LOG(ERR, "ixgbe_rxq_vec_setup: could not allocate one mbuf");
> +		return -1;
> +	}
> +	/* nb_segs, refcnt, data_off and buf_len are already set */
> +	mb_def->port = rxq->port_id;
> 
>  	/* prevent compiler reordering: rearm_data covers previous fields */
>  	rte_compiler_barrier();

I don't think we need it here.

> -	rxq->mbuf_initializer = *((uint64_t *)&mb_def.rearm_data);
> +	rxq->mbuf_initializer = *((uint64_t *)&mb_def->rearm_data);
> +
> +	rte_pktmbuf_free(mb_def);
> +
>  	return 0;
>  }
> 
> --
> 2.1.3

Somy vote -  NACK for the whole series.
Konstantin