Re: [dpdk-dev] [PATCH] mlx4: use dummy rxqs when a non-pow2 number is requested

["Wiles, Keith" <keith.wiles@intel.com>]

Sent from my iPhone

> On Mar 21, 2016, at 11:10 AM, Olivier Matz <olivier.matz@6wind.com> wrote:
> 
> When using RSS, the number of rxqs has to be a power of two.
> This is a problem because there is no API is dpdk that makes
> the application aware of that.
> 
> A good compromise is to allow the application to request a
> number of rxqs that is not a power of 2, but having inactive
> queues that will never receive packets. In this configuration,
> a warning will be issued to users to let them know that
> this is not an optimal configuration.

Not sure I like this solution. I think an error should be returned with a log message instead. What if the next driver needs power of three or must be odd or even number. 

The bigger problem is the application is no longer portable for any given nic configuration.

We need a method for the application to query the system for these types of information. But as we do not have that API we need to just error the request off.

> 
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> ---
> drivers/net/mlx4/mlx4.c | 27 +++++++++++++++++----------
> 1 file changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/mlx4/mlx4.c b/drivers/net/mlx4/mlx4.c
> index cc4e9aa..eaf06db 100644
> --- a/drivers/net/mlx4/mlx4.c
> +++ b/drivers/net/mlx4/mlx4.c
> @@ -698,7 +698,7 @@ txq_cleanup(struct txq *txq);
> 
> static int
> rxq_setup(struct rte_eth_dev *dev, struct rxq *rxq, uint16_t desc,
> -      unsigned int socket, const struct rte_eth_rxconf *conf,
> +      unsigned int socket, int inactive, const struct rte_eth_rxconf *conf,
>      struct rte_mempool *mp);
> 
> static void
> @@ -734,12 +734,12 @@ dev_configure(struct rte_eth_dev *dev)
>    }
>    if (rxqs_n == priv->rxqs_n)
>        return 0;
> -    if ((rxqs_n & (rxqs_n - 1)) != 0) {
> -        ERROR("%p: invalid number of RX queues (%u),"
> -              " must be a power of 2",
> +    if (!rte_is_power_of_2(rxqs_n)) {
> +        WARN("%p: number of RX queues (%u), must be a"
> +              " power of 2: remaining queues will be inactive",
>              (void *)dev, rxqs_n);
> -        return EINVAL;
>    }
> +
>    INFO("%p: RX queues number update: %u -> %u",
>         (void *)dev, priv->rxqs_n, rxqs_n);
>    /* If RSS is enabled, disable it first. */
> @@ -775,7 +775,7 @@ dev_configure(struct rte_eth_dev *dev)
>    priv->rss = 1;
>    tmp = priv->rxqs_n;
>    priv->rxqs_n = rxqs_n;
> -    ret = rxq_setup(dev, &priv->rxq_parent, 0, 0, NULL, NULL);
> +    ret = rxq_setup(dev, &priv->rxq_parent, 0, 0, 0, NULL, NULL);
>    if (!ret)
>        return 0;
>    /* Failure, rollback. */
> @@ -3466,7 +3466,8 @@ rxq_setup_qp_rss(struct priv *priv, struct ibv_cq *cq, uint16_t desc,
>        attr.qpg.qpg_type = IBV_EXP_QPG_PARENT;
>        /* TSS isn't necessary. */
>        attr.qpg.parent_attrib.tss_child_count = 0;
> -        attr.qpg.parent_attrib.rss_child_count = priv->rxqs_n;
> +        attr.qpg.parent_attrib.rss_child_count =
> +            rte_align32pow2(priv->rxqs_n + 1) >> 1;
>        DEBUG("initializing parent RSS queue");
>    } else {
>        attr.qpg.qpg_type = IBV_EXP_QPG_CHILD_RX;
> @@ -3689,6 +3690,9 @@ skip_rtr:
>  *   Number of descriptors to configure in queue.
>  * @param socket
>  *   NUMA socket on which memory must be allocated.
> + * @param inactive
> + *   If true, the queue is disabled because its index is higher or
> + *   equal to the real number of queues, which must be a power of 2.
>  * @param[in] conf
>  *   Thresholds parameters.
>  * @param mp
> @@ -3699,7 +3703,7 @@ skip_rtr:
>  */
> static int
> rxq_setup(struct rte_eth_dev *dev, struct rxq *rxq, uint16_t desc,
> -      unsigned int socket, const struct rte_eth_rxconf *conf,
> +      unsigned int socket, int inactive, const struct rte_eth_rxconf *conf,
>      struct rte_mempool *mp)
> {
>    struct priv *priv = dev->data->dev_private;
> @@ -3800,7 +3804,7 @@ skip_mr:
>    DEBUG("priv->device_attr.max_sge is %d",
>          priv->device_attr.max_sge);
> #ifdef RSS_SUPPORT
> -    if (priv->rss)
> +    if (priv->rss && !inactive)
>        tmpl.qp = rxq_setup_qp_rss(priv, tmpl.cq, desc, parent,
>                       tmpl.rd);
>    else
> @@ -3936,6 +3940,7 @@ mlx4_rx_queue_setup(struct rte_eth_dev *dev, uint16_t idx, uint16_t desc,
> {
>    struct priv *priv = dev->data->dev_private;
>    struct rxq *rxq = (*priv->rxqs)[idx];
> +    int inactive = 0;
>    int ret;
> 
>    if (mlx4_is_secondary())
> @@ -3967,7 +3972,9 @@ mlx4_rx_queue_setup(struct rte_eth_dev *dev, uint16_t idx, uint16_t desc,
>            return -ENOMEM;
>        }
>    }
> -    ret = rxq_setup(dev, rxq, desc, socket, conf, mp);
> +    if (idx >= rte_align32pow2(priv->rxqs_n + 1) >> 1)
> +        inactive = 1;
> +    ret = rxq_setup(dev, rxq, desc, socket, inactive, conf, mp);
>    if (ret)
>        rte_free(rxq);
>    else {
> -- 
> 2.1.4
>