[ovs-dev] [PATCH v8 11/13] netdev-dpdk: copy large packet to multi-seg. mbufs

[Eelco Chaudron]

On 11 Jun 2018, at 18:21, Tiago Lam wrote:

> From: Mark Kavanagh <mark.b.kavanagh at intel.com>
>
> Currently, packets are only copied to a single segment in the function
> dpdk_do_tx_copy(). This could be an issue in the case of jumbo frames,
> particularly when multi-segment mbufs are involved.
>
> This patch calculates the number of segments needed by a packet and
> copies the data to each segment.
>
> A new function, dpdk_buf_alloc(), has also been introduced as a 
> wrapper
> around the nonpmd_mp_mutex to serialise allocations from a non-pmd
> context.
>
> Co-authored-by: Michael Qiu <qiudayu at chinac.com>
> Co-authored-by: Tiago Lam <tiago.lam at intel.com>
>
> Signed-off-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
> Signed-off-by: Michael Qiu <qiudayu at chinac.com>
> Signed-off-by: Tiago Lam <tiago.lam at intel.com>
> ---
>  lib/netdev-dpdk.c | 94 
> +++++++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 84 insertions(+), 10 deletions(-)
>
> diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
> index 9b1fb9a..0079e28 100644
> --- a/lib/netdev-dpdk.c
> +++ b/lib/netdev-dpdk.c
> @@ -515,6 +515,22 @@ dpdk_rte_mzalloc(size_t sz)
>      return rte_zmalloc(OVS_VPORT_DPDK, sz, OVS_CACHE_LINE_SIZE);
>  }
>
> +static struct rte_mbuf *
> +dpdk_buf_alloc(struct rte_mempool *mp)
> +{
> +    if (!dpdk_thread_is_pmd()) {
> +        ovs_mutex_lock(&nonpmd_mp_mutex);
Can you explain why the lock is needed here for non PMD threads?
> +    }
> +
> +    struct rte_mbuf *mbuf = rte_pktmbuf_alloc(mp);
> +
> +    if (!dpdk_thread_is_pmd()) {
> +        ovs_mutex_unlock(&nonpmd_mp_mutex);
> +    }
> +
> +    return mbuf;
> +}
> +
>  void
>  free_dpdk_buf(struct dp_packet *p)
>  {
> @@ -2167,6 +2183,71 @@ out:
>      }
>  }
>
> +static int

a bool, true for success might be more usefull here.

> +dpdk_prep_tx_buf(struct dp_packet *packet, struct rte_mbuf **head,
> +                 struct rte_mempool *mp)

Maybe the function name should be more what it's doing, i.e 
dpdk_clone_dp_packet_to_mbuf().

> +{
> +    struct rte_mbuf *temp;
> +    uint32_t size = dp_packet_size(packet);
> +    uint16_t max_data_len, data_len;
> +    uint32_t nb_segs = 0;
> +    int i;
> +
> +    temp = *head = dpdk_buf_alloc(mp);
> +    if (OVS_UNLIKELY(!temp)) {
> +        return 1;
> +    }
> +
> +    /* All new allocated mbuf's max data len is the same */
> +    max_data_len = temp->buf_len - temp->data_off;
> +
> +    /* Calculate # of output mbufs. */
> +    nb_segs = size / max_data_len;
> +    if (size % max_data_len) {
> +        nb_segs = nb_segs + 1;
> +    }
> +
> +    /* Allocate additional mbufs when multiple output mbufs required. 
> */
> +    for (i = 1; i < nb_segs; i++) {
> +        temp->next = dpdk_buf_alloc(mp);
> +        if (!temp->next) {
> +            free_dpdk_buf((struct dp_packet *) *head);
> +            *head = NULL;
> +            break;
> +        }
> +        temp = temp->next;
> +    }
> +    /* We have to do a copy for now */
> +    rte_pktmbuf_pkt_len(*head) = size;
> +    temp = *head;
> +
> +    data_len = size < max_data_len ? size: max_data_len;

Can we use max_data_len to copy? It's only valid if rte_pktmbuf_mtod() 
returns the first byte, but after alloc it's 
rte_pktmbuf_reset_headroom(). So we will overwrite invalid memory.

> +    if (packet->source == DPBUF_DPDK) {
> +        *head = &(packet->mbuf);
> +        while (temp && head && size > 0) {
> +            rte_memcpy(rte_pktmbuf_mtod(temp, void *),
> +                    dp_packet_data((struct dp_packet *)head), 
> data_len);

Here you assume source and destination mbuf sizes are the same...
Also use container_of for "(struct dp_packet *)head)"

> +            rte_pktmbuf_data_len(temp) = data_len;
> +            *head = (*head)->next;
> +            size = size - data_len;
> +            data_len =  size < max_data_len ? size: max_data_len;
> +            temp = temp->next;
> +        }
> +    } else {

Why not use dp_packet_mbuf_write() here?

> +        int offset = 0;
> +        while (temp && size > 0) {
> +            memcpy(rte_pktmbuf_mtod(temp, void *),
> +                    dp_packet_at(packet, offset, data_len), 
> data_len);
> +            rte_pktmbuf_data_len(temp) = data_len;
> +            temp = temp->next;
> +            size = size - data_len;
> +            offset += data_len;
> +            data_len = size < max_data_len ? size: max_data_len;
> +        }
> +    }
> +    return 0;
> +}
> +
>  /* Tx function. Transmit packets indefinitely */
>  static void
>  dpdk_do_tx_copy(struct netdev *netdev, int qid, struct 
> dp_packet_batch *batch)
> @@ -2183,6 +2264,7 @@ dpdk_do_tx_copy(struct netdev *netdev, int qid, 
> struct dp_packet_batch *batch)
>      struct rte_mbuf *pkts[PKT_ARRAY_SIZE];
>      uint32_t cnt = batch_cnt;
>      uint32_t dropped = 0;
> +    uint32_t i;
>
>      if (dev->type != DPDK_DEV_VHOST) {
>          /* Check if QoS has been configured for this netdev. */
> @@ -2193,27 +2275,19 @@ dpdk_do_tx_copy(struct netdev *netdev, int 
> qid, struct dp_packet_batch *batch)
>
>      uint32_t txcnt = 0;
>
> -    for (uint32_t i = 0; i < cnt; i++) {
> +    for (i = 0; i < cnt; i++) {
>          struct dp_packet *packet = batch->packets[i];
>          uint32_t size = dp_packet_size(packet);
> -
>          if (OVS_UNLIKELY(size > dev->max_packet_len)) {
>              VLOG_WARN_RL(&rl, "Too big size %u max_packet_len %d",
>                           size, dev->max_packet_len);
> -
>              dropped++;
>              continue;
>          }
> -
> -        pkts[txcnt] = rte_pktmbuf_alloc(dev->mp);
> -        if (OVS_UNLIKELY(!pkts[txcnt])) {
> +        if (dpdk_prep_tx_buf(packet, &pkts[txcnt], dev->mp)) {
>              dropped += cnt - i;
>              break;
>          }
> -
> -        /* We have to do a copy for now */
> -        memcpy(rte_pktmbuf_mtod(pkts[txcnt], void *),
> -               dp_packet_data(packet), size);
>          dp_packet_set_size((struct dp_packet *)pkts[txcnt], size);
>          dp_packet_copy_mbuf_flags((struct dp_packet *)pkts[txcnt], 
> packet);
>
> -- 
> 2.7.4