[ovs-dev] [RFC v5 7/8] netdev-dpdk: copy large packet to multi-seg. mbufs

[Tiago Lam]

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.

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 | 78 ++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 68 insertions(+), 10 deletions(-)

diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
index c9de742..4c6a3c0 100644
--- a/lib/netdev-dpdk.c
+++ b/lib/netdev-dpdk.c
@@ -2101,6 +2101,71 @@ out:
     }
 }
 
+static int
+dpdk_prep_tx_buf(struct dp_packet *packet, struct rte_mbuf **head,
+                 struct rte_mempool *mp)
+{
+    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 = rte_pktmbuf_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 = rte_pktmbuf_alloc(mp);
+        if (!temp->next) {
+            rte_pktmbuf_free(*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;
+    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);
+            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 {
+        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)
@@ -2117,6 +2182,7 @@ 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. */
@@ -2127,27 +2193,19 @@ 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