Re: [PATCH v4 6/7] virtio: simple tx routine

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 22 Oct 2015 20:09:50 +0800
Huawei Xie <huawei.xie@intel.com> wrote:

> Changes in v4:
> - move virtio_xmit_cleanup ahead to free descriptors earlier
> 
> Changes in v3:
> - Remove return at the end of void function
> - Remove always_inline attribute for virtio_xmit_cleanup
> bulk free of mbufs when clean used ring.
> shift operation of idx could be saved if vq_free_cnt means
> free slots rather than free descriptors.
> 
> TODO: rearrange vq data structure, pack the stats var together so that we
> could use one vec instruction to update all of them.
> 
> Signed-off-by: Huawei Xie <huawei.xie@intel.com>
> ---
>  drivers/net/virtio/virtio_ethdev.h      |  3 ++
>  drivers/net/virtio/virtio_rxtx_simple.c | 93 +++++++++++++++++++++++++++++++++
>  2 files changed, 96 insertions(+)
> 
> diff --git a/drivers/net/virtio/virtio_ethdev.h b/drivers/net/virtio/virtio_ethdev.h
> index d7797ab..ae2d47d 100644
> --- a/drivers/net/virtio/virtio_ethdev.h
> +++ b/drivers/net/virtio/virtio_ethdev.h
> @@ -111,6 +111,9 @@ uint16_t virtio_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
>  uint16_t virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
>  		uint16_t nb_pkts);
>  
> +uint16_t virtio_xmit_pkts_simple(void *tx_queue, struct rte_mbuf **tx_pkts,
> +		uint16_t nb_pkts);
> +
>  /*
>   * The VIRTIO_NET_F_GUEST_TSO[46] features permit the host to send us
>   * frames larger than 1514 bytes. We do not yet support software LRO
> diff --git a/drivers/net/virtio/virtio_rxtx_simple.c b/drivers/net/virtio/virtio_rxtx_simple.c
> index ef17562..79b4f7f 100644
> --- a/drivers/net/virtio/virtio_rxtx_simple.c
> +++ b/drivers/net/virtio/virtio_rxtx_simple.c
> @@ -288,6 +288,99 @@ virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
>  	return nb_pkts_received;
>  }
>  
> +#define VIRTIO_TX_FREE_THRESH 32
> +#define VIRTIO_TX_MAX_FREE_BUF_SZ 32
> +#define VIRTIO_TX_FREE_NR 32
> +/* TODO: vq->tx_free_cnt could mean num of free slots so we could avoid shift */
> +static inline void
> +virtio_xmit_cleanup(struct virtqueue *vq)
> +{
> +	uint16_t i, desc_idx;
> +	int nb_free = 0;
> +	struct rte_mbuf *m, *free[VIRTIO_TX_MAX_FREE_BUF_SZ];
> +
> +	desc_idx = (uint16_t)(vq->vq_used_cons_idx &
> +		((vq->vq_nentries >> 1) - 1));
> +	free[0] = (struct rte_mbuf *)vq->vq_descx[desc_idx++].cookie;
> +	nb_free = 1;
> +
> +	for (i = 1; i < VIRTIO_TX_FREE_NR; i++) {
> +		m = (struct rte_mbuf *)vq->vq_descx[desc_idx++].cookie;
> +		if (likely(m->pool == free[0]->pool))
> +			free[nb_free++] = m;
> +		else {
> +			rte_mempool_put_bulk(free[0]->pool, (void **)free,
> +				nb_free);
> +			free[0] = m;
> +			nb_free = 1;
> +		}
> +	}
> +
> +	rte_mempool_put_bulk(free[0]->pool, (void **)free, nb_free);
> +	vq->vq_used_cons_idx += VIRTIO_TX_FREE_NR;
> +	vq->vq_free_cnt += (VIRTIO_TX_FREE_NR << 1);
> +}

I think you need to handle refcount, here is a similar patch
for ixgbe.

Subject: ixgbe: speed up transmit

Coalesce transmit buffers and put them back into the pool
in one burst.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

--- a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
+++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
@@ -120,12 +120,16 @@ rte_rxmbuf_alloc(struct rte_mempool *mp)
  * Check for descriptors with their DD bit set and free mbufs.
  * Return the total number of buffers freed.
  */
+#define TX_FREE_BULK 32
+
 static inline int __attribute__((always_inline))
 ixgbe_tx_free_bufs(struct ixgbe_tx_queue *txq)
 {
 	struct ixgbe_tx_entry *txep;
 	uint32_t status;
-	int i;
+	int i, n = 0;
+	struct rte_mempool *txpool = NULL;
+	struct rte_mbuf *free_list[TX_FREE_BULK];
 
 	/* check DD bit on threshold descriptor */
 	status = txq->tx_ring[txq->tx_next_dd].wb.status;
@@ -138,20 +142,26 @@ ixgbe_tx_free_bufs(struct ixgbe_tx_queue
 	 */
 	txep = &(txq->sw_ring[txq->tx_next_dd - (txq->tx_rs_thresh - 1)]);
 
-	/* free buffers one at a time */
-	if ((txq->txq_flags & (uint32_t)ETH_TXQ_FLAGS_NOREFCOUNT) != 0) {
-		for (i = 0; i < txq->tx_rs_thresh; ++i, ++txep) {
-			txep->mbuf->next = NULL;
-			rte_mempool_put(txep->mbuf->pool, txep->mbuf);
-			txep->mbuf = NULL;
-		}
-	} else {
-		for (i = 0; i < txq->tx_rs_thresh; ++i, ++txep) {
-			rte_pktmbuf_free_seg(txep->mbuf);
-			txep->mbuf = NULL;
+	for (i = 0; i < txq->tx_rs_thresh; ++i, ++txep) {
+		struct rte_mbuf *m;
+
+		/* free buffers one at a time */
+		m = __rte_pktmbuf_prefree_seg(txep->mbuf);
+		txep->mbuf = NULL;
+
+		if (n >= TX_FREE_BULK  ||
+		    (n > 0 && m->pool != txpool)) {
+			rte_mempool_put_bulk(txpool, (void **)free_list, n);
+			n = 0;
 		}
+
+		txpool = m->pool;
+		free_list[n++] = m;
 	}
 
+	if (n > 0)
+		rte_mempool_put_bulk(txpool, (void **)free_list, n);
+
 	/* buffers were freed, update counters */
 	txq->nb_tx_free = (uint16_t)(txq->nb_tx_free + txq->tx_rs_thresh);
 	txq->tx_next_dd = (uint16_t)(txq->tx_next_dd + txq->tx_rs_thresh);