Re: [PATCH] ixgbe: fix checking for tx_free_thresh

[Zoltan Kiss <zoltan.kiss@linaro.org>]

Hi,

Anyone would like to review this patch? Venky sent a NAK, but I've 
explained to him why it is a bug.

Regards,

Zoltan

On 27/05/15 21:12, Zoltan Kiss 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);
>