Re: [dpdk-dev] [PATCH] ixgbe: fix checking for tx_free_thresh

["Venkatesan, Venky" <venky.venkatesan@intel.com>]

NAK. This causes more (unsuccessful) cleanup attempts on the descriptor ring. What is motivating this change? 

Regards,
Venky


> On May 28, 2015, at 1:42 AM, Zoltan Kiss <zoltan.kiss@linaro.org> wrote:
> 
> This check doesn't do what's required by rte_eth_tx_burst:
> "When the number of previously sent packets reached the "minimum transmit
> packets to free" threshold"
> 
> This can cause problems when txq->tx_free_thresh + [number of elements in the
> pool] < txq->nb_tx_desc.
> 
> Signed-off-by: Zoltan Kiss <zoltan.kiss@linaro.org>
> ---
> drivers/net/ixgbe/ixgbe_rxtx.c     | 4 ++--
> drivers/net/ixgbe/ixgbe_rxtx_vec.c | 2 +-
> 2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
> index 4f9ab22..b70ed8c 100644
> --- a/drivers/net/ixgbe/ixgbe_rxtx.c
> +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
> @@ -250,10 +250,10 @@ tx_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
> 
>    /*
>     * Begin scanning the H/W ring for done descriptors when the
> -     * number of available descriptors drops below tx_free_thresh.  For
> +     * number of in flight descriptors reaches tx_free_thresh. For
>     * each done descriptor, free the associated buffer.
>     */
> -    if (txq->nb_tx_free < txq->tx_free_thresh)
> +    if ((txq->nb_tx_desc - txq->nb_tx_free) > txq->tx_free_thresh)
>        ixgbe_tx_free_bufs(txq);
> 
>    /* Only use descriptors that are available */
> diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec.c b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
> index abd10f6..f91c698 100644
> --- a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
> +++ b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
> @@ -598,7 +598,7 @@ ixgbe_xmit_pkts_vec(void *tx_queue, struct rte_mbuf **tx_pkts,
>    if (unlikely(nb_pkts > RTE_IXGBE_VPMD_TX_BURST))
>        nb_pkts = RTE_IXGBE_VPMD_TX_BURST;
> 
> -    if (txq->nb_tx_free < txq->tx_free_thresh)
> +    if ((txq->nb_tx_desc - txq->nb_tx_free) > txq->tx_free_thresh)
>        ixgbe_tx_free_bufs(txq);
> 
>    nb_commit = nb_pkts = (uint16_t)RTE_MIN(txq->nb_tx_free, nb_pkts);
> -- 
> 1.9.1
>