> -----Original Message-----
> From: Xing, Beilei
> Sent: Thursday, October 25, 2018 2:41 AM
> To: Zhang, Qi Z <qi.z.zh...@intel.com>
> Cc: dev@dpdk.org; sta...@dpdk.org
> Subject: [PATCH] net/i40e: fix Rx instability with vector mode
>
> Previously, there is instability during vector Rx if descriptor number is not
> power of 2, e.g. process hang and some Rx packets are unexpectedly empty.
> That's because vector Rx mode assumes Rx descriptor number is power of 2
> when doing bit mask.
> This patch allows vector mode only when the number of Rx descriptor is
> power of 2.
>
> Fixes: 8e109464c022 ("i40e: allow vector Rx and Tx usage")
> Fixes: a3c83a2527e1 ("net/i40e: enable runtime queue setup")
> Cc: sta...@dpdk.org
>
> Signed-off-by: Beilei Xing <beilei.x...@intel.com>
> ---
> doc/guides/nics/i40e.rst | 7 +++++++
> drivers/net/i40e/i40e_rxtx.c | 18 +++++++++++++++++-
> 2 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/doc/guides/nics/i40e.rst b/doc/guides/nics/i40e.rst index
> ab3928a..bfacbd1 100644
> --- a/doc/guides/nics/i40e.rst
> +++ b/doc/guides/nics/i40e.rst
> @@ -172,6 +172,13 @@ Runtime Config Options
>
> -w 84:00.0,use-latest-supported-vec=1
>
> +Vector RX Pre-conditions
> +~~~~~~~~~~~~~~~~~~~~~~~~
> +For Vector RX it is assumed that the number of descriptor rings will be
> +a power of 2. With this pre-condition, the ring pointer can easily
> +scroll back to the head after hitting the tail without a conditional
> +check. In addition Vector RX can use this assumption to do a bit mask using
> ``ring_size - 1``.
> +
> Driver compilation and testing
> ------------------------------
>
> diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c index
> a827456..aa46d83 100644
> --- a/drivers/net/i40e/i40e_rxtx.c
> +++ b/drivers/net/i40e/i40e_rxtx.c
> @@ -1735,10 +1735,17 @@ i40e_dev_rx_queue_setup_runtime(struct
> rte_eth_dev *dev,
> * i40e_set_rx_function.
> */
> ad->rx_bulk_alloc_allowed = true;
> - ad->rx_vec_allowed = true;
> dev->data->scattered_rx = use_scattered_rx;
> if (use_def_burst_func)
> ad->rx_bulk_alloc_allowed = false;
> + /**
> + * Vector mode is allowed only when number of Rx queue
> + * descriptor is a power of 2.
> + */
> + if ((rxq->nb_rx_desc & (rxq->nb_rx_desc - 1)))
> + ad->rx_vec_allowed = false;
> + else
> + ad->rx_vec_allowed = true;
> i40e_set_rx_function(dev);
> return 0;
> }
> @@ -1811,6 +1818,15 @@ i40e_dev_rx_queue_setup(struct rte_eth_dev
> *dev,
> return -EINVAL;
> }
>
> + /**
> + * Vector mode is allowed only when number of Rx queue
> + * descriptor is a power of 2.
> + */
> + if ((nb_desc & (nb_desc - 1)))
> + ad->rx_vec_allowed = false;
> + else
> + ad->rx_vec_allowed = true;
rx_vec_allowed will be overwritten unexpectedly for multi-queues case
We may only to overwrite with below condition check.
If (first_queue || ad->rx_vec_allowed)
ad->rx_vec_allowed = ! (nb_desc & (nb_desc - 1));
> +
> /* Free memory if needed */
> if (dev->data->rx_queues[queue_idx]) {
> i40e_dev_rx_queue_release(dev->data->rx_queues[queue_idx]);
> --
> 2.5.5
