Re: [dpdk-dev] [PATCH v6 3/4] net/ixgbe: cleanup Tx buffers

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi,

> Add support to the ixgbe driver for the API rte_eth_tx_done_cleanup
> to force free consumed buffers on Tx ring.
> 
> Signed-off-by: Chenxu Di <chenxux.di@intel.com>
> ---
>  drivers/net/ixgbe/ixgbe_ethdev.c |   2 +
>  drivers/net/ixgbe/ixgbe_rxtx.c   | 116 +++++++++++++++++++++++++++++++
>  drivers/net/ixgbe/ixgbe_rxtx.h   |   2 +
>  3 files changed, 120 insertions(+)
> 
> diff --git a/drivers/net/ixgbe/ixgbe_ethdev.c b/drivers/net/ixgbe/ixgbe_ethdev.c
> index 2c6fd0f13..0091405db 100644
> --- a/drivers/net/ixgbe/ixgbe_ethdev.c
> +++ b/drivers/net/ixgbe/ixgbe_ethdev.c
> @@ -601,6 +601,7 @@ static const struct eth_dev_ops ixgbe_eth_dev_ops = {
>  	.udp_tunnel_port_add  = ixgbe_dev_udp_tunnel_port_add,
>  	.udp_tunnel_port_del  = ixgbe_dev_udp_tunnel_port_del,
>  	.tm_ops_get           = ixgbe_tm_ops_get,
> +	.tx_done_cleanup      = ixgbe_tx_done_cleanup,

Don't see how we can have one tx_done_cleanup() for different tx functions?
Vector and scalar TX path use different  format for sw_ring[] entries.
Also offload and simile TX paths use different method to track used/free descriptors,
and use different functions to free them:
offload uses tx_entry next_id, last_id plus txq. last_desc_cleaned, while
simple TX paths use tx_next_dd. 


>  };
> 
>  /*
> @@ -649,6 +650,7 @@ static const struct eth_dev_ops ixgbevf_eth_dev_ops = {
>  	.reta_query           = ixgbe_dev_rss_reta_query,
>  	.rss_hash_update      = ixgbe_dev_rss_hash_update,
>  	.rss_hash_conf_get    = ixgbe_dev_rss_hash_conf_get,
> +	.tx_done_cleanup      = ixgbe_tx_done_cleanup,
>  };
> 
>  /* store statistics names and its offset in stats structure */
> diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
> index fa572d184..520b9c756 100644
> --- a/drivers/net/ixgbe/ixgbe_rxtx.c
> +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
> @@ -2306,6 +2306,122 @@ ixgbe_tx_queue_release_mbufs(struct ixgbe_tx_queue *txq)
>  	}
>  }
> 
> +int ixgbe_tx_done_cleanup(void *q, uint32_t free_cnt)

That seems to work only for offload(full) TX path (ixgbe_xmit_pkts).
Simple(fast) path seems not covered by this function.

> +{
> +	struct ixgbe_tx_queue *txq = (struct ixgbe_tx_queue *)q;
> +	struct ixgbe_tx_entry *sw_ring;
> +	volatile union ixgbe_adv_tx_desc *txr;
> +	uint16_t tx_first; /* First segment analyzed. */
> +	uint16_t tx_id;    /* Current segment being processed. */
> +	uint16_t tx_last;  /* Last segment in the current packet. */
> +	uint16_t tx_next;  /* First segment of the next packet. */
> +	int count;
> +
> +	if (txq == NULL)
> +		return -ENODEV;
> +
> +	count = 0;
> +	sw_ring = txq->sw_ring;
> +	txr = txq->tx_ring;
> +
> +	/*
> +	 * tx_tail is the last sent packet on the sw_ring. Goto the end
> +	 * of that packet (the last segment in the packet chain) and
> +	 * then the next segment will be the start of the oldest segment
> +	 * in the sw_ring. 

Not sure I understand the sentence above.
tx_tail is the value of TDT HW register (most recently armed by SW TD).
last_id  is the index of last descriptor for multi-seg packet.
next_id is just the index of next descriptor in HW TD ring.
How do you conclude that it will be the ' oldest segment in the sw_ring'?

Another question why do you need to write your own functions?
Why can't you reuse existing ixgbe_xmit_cleanup() for full(offload) path
and  ixgbe_tx_free_bufs() for simple path?
Yes,  ixgbe_xmit_cleanup() doesn't free mbufs, but at least it could be used
to determine finished TX descriptors.
Based on that you can you can free appropriate sw_ring[] entries.

>This is the first packet that will be
> +	 * attempted to be freed.
> +	 */
> +
> +	/* Get last segment in most recently added packet. */
> +	tx_last = sw_ring[txq->tx_tail].last_id;
> +
> +	/* Get the next segment, which is the oldest segment in ring. */
> +	tx_first = sw_ring[tx_last].next_id;
> +
> +	/* Set the current index to the first. */
> +	tx_id = tx_first;
> +
> +	/*
> +	 * Loop through each packet. For each packet, verify that an
> +	 * mbuf exists and that the last segment is free. If so, free
> +	 * it and move on.
> +	 */
> +	while (1) {
> +		tx_last = sw_ring[tx_id].last_id;
> +
> +		if (sw_ring[tx_last].mbuf) {
> +			if (!(txr[tx_last].wb.status &
> +				IXGBE_TXD_STAT_DD))
> +				break;
> +
> +			/* Get the start of the next packet. */
> +			tx_next = sw_ring[tx_last].next_id;
> +
> +			/*
> +			 * Loop through all segments in a
> +			 * packet.
> +			 */
> +			do {
> +				rte_pktmbuf_free_seg(sw_ring[tx_id].mbuf);
> +				sw_ring[tx_id].mbuf = NULL;
> +				sw_ring[tx_id].last_id = tx_id;
> +
> +				/* Move to next segment. */
> +				tx_id = sw_ring[tx_id].next_id;
> +
> +			} while (tx_id != tx_next);
> +
> +			/*
> +			 * Increment the number of packets
> +			 * freed.
> +			 */
> +			count++;
> +
> +			if (unlikely(count == (int)free_cnt))
> +				break;
> +		} else {
> +			/*
> +			 * There are multiple reasons to be here:
> +			 * 1) All the packets on the ring have been
> +			 *    freed - tx_id is equal to tx_first
> +			 *    and some packets have been freed.
> +			 *    - Done, exit
> +			 * 2) Interfaces has not sent a rings worth of
> +			 *    packets yet, so the segment after tail is
> +			 *    still empty. Or a previous call to this
> +			 *    function freed some of the segments but
> +			 *    not all so there is a hole in the list.
> +			 *    Hopefully this is a rare case.
> +			 *    - Walk the list and find the next mbuf. If
> +			 *      there isn't one, then done.
> +			 */
> +			if (likely(tx_id == tx_first && count != 0))
> +				break;
> +
> +			/*
> +			 * Walk the list and find the next mbuf, if any.
> +			 */
> +			do {
> +				/* Move to next segment. */
> +				tx_id = sw_ring[tx_id].next_id;
> +
> +				if (sw_ring[tx_id].mbuf)
> +					break;
> +
> +			} while (tx_id != tx_first);
> +
> +			/*
> +			 * Determine why previous loop bailed. If there
> +			 * is not an mbuf, done.
> +			 */
> +			if (sw_ring[tx_id].mbuf == NULL)
> +				break;
> +		}
> +	}
> +
> +	return count;
> +}
> +
>  static void __attribute__((cold))
>  ixgbe_tx_free_swring(struct ixgbe_tx_queue *txq)
>  {
> diff --git a/drivers/net/ixgbe/ixgbe_rxtx.h b/drivers/net/ixgbe/ixgbe_rxtx.h
> index 505d344b9..2c3770af6 100644
> --- a/drivers/net/ixgbe/ixgbe_rxtx.h
> +++ b/drivers/net/ixgbe/ixgbe_rxtx.h
> @@ -285,6 +285,8 @@ int ixgbe_rx_vec_dev_conf_condition_check(struct rte_eth_dev *dev);
>  int ixgbe_rxq_vec_setup(struct ixgbe_rx_queue *rxq);
>  void ixgbe_rx_queue_release_mbufs_vec(struct ixgbe_rx_queue *rxq);
> 
> +int ixgbe_tx_done_cleanup(void *txq, uint32_t free_cnt);
> +
>  extern const uint32_t ptype_table[IXGBE_PACKET_TYPE_MAX];
>  extern const uint32_t ptype_table_tn[IXGBE_PACKET_TYPE_TN_MAX];
> 
> --
> 2.17.1