[PATCH v2] net/ixgbe: fix min Rx/Tx descriptors

[Bruce Richardson]

On Tue, Feb 25, 2025 at 09:12:36AM +0000, Mingjin Ye wrote:
> The minimum free packet threshold (tx_free_thresh) and the minimum RS bit
> threshold (tx_rs_thresh) both have a default value of 32. Therefore, the
> default minimum number of ring descriptors value is 64.
> 
> For reference, see "Configuration of Transmit Queues" in
> doc/guides/prog_guide/ethdev/ethdev.rst
> 
> Fixes: dee5f1fd5fc7 ("ixgbe: get queue info and descriptor limits")
> Cc: stable at dpdk.org
> 
> Signed-off-by: Mingjin Ye <mingjinx.ye at intel.com>
> ---
> v2: Change doc.
> ---
>  doc/guides/nics/ixgbe.rst            | 5 +++--
>  drivers/net/intel/ixgbe/ixgbe_rxtx.h | 2 +-
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/guides/nics/ixgbe.rst b/doc/guides/nics/ixgbe.rst
> index c5c6a6c34b..aaed324e15 100644
> --- a/doc/guides/nics/ixgbe.rst
> +++ b/doc/guides/nics/ixgbe.rst
> @@ -68,11 +68,12 @@ Ensure that the following pre-conditions are satisfied:
>  
>  *   (rxq->nb_rx_desc % rxq->rx_free_thresh) == 0
>  
> -*   rxq->nb_rx_desc  < (IXGBE_MAX_RING_DESC - RTE_PMD_IXGBE_RX_MAX_BURST)
> +*   rxq->nb_rx_desc >= IXGBE_MIN_RING_DESC
> +
> +*   rxq->nb_rx_desc <= IXGBE_MAX_RING_DESC
>  
>  These conditions are checked in the code.
>  
> -Scattered packets are not supported in this mode.
>  If an incoming packet is greater than the maximum acceptable length of one "mbuf" data size (by default, the size is 2 KB),
>  vPMD for RX would be disabled.
>  

These two lines in the doc should be removed as well, since they also imply
the unavailability of scattered Rx.
Fixing this by dropping them on apply.

> diff --git a/drivers/net/intel/ixgbe/ixgbe_rxtx.h b/drivers/net/intel/ixgbe/ixgbe_rxtx.h
> index 278f665108..54569c7ade 100644
> --- a/drivers/net/intel/ixgbe/ixgbe_rxtx.h
> +++ b/drivers/net/intel/ixgbe/ixgbe_rxtx.h
> @@ -26,7 +26,7 @@
>   * descriptors should meet the following condition:
>   *      (num_ring_desc * sizeof(rx/tx descriptor)) % 128 == 0
>   */
> -#define	IXGBE_MIN_RING_DESC	32
> +#define	IXGBE_MIN_RING_DESC	64
>  #define	IXGBE_MAX_RING_DESC	8192
>  
>  #define RTE_PMD_IXGBE_TX_MAX_BURST 32
> -- 
> 2.25.1
> 

Acked-by: Bruce Richardson <bruce.richardson at intel.com>

Applied to dpdk-next-net-intel.

Thanks,
/Bruce