[ovs-dev] [RFC v7 09/13] dp-packet: Handle multi-seg mbufs in resize__().

Tiago Lam tiago.lam at intel.com
Wed May 23 16:47:24 UTC 2018


When enabled with DPDK OvS relies on mbufs allocated by mempools to
receive and output data on DPDK ports. Until now, each OvS dp_packet has
only one mbuf associated, which is allocated with the maximum possible
size, taking the MTU into account. This approach, however, doesn't allow
us to increase the allocated size in an mbuf, if needed, since an mbuf
is allocated and initialised upon mempool creation. Thus, in the current
implementatin this is dealt with by calling OVS_NOTEACHED() and
terminating OvS.

To avoid this, and allow the allocated size to be increased, multiple
mbufs can be linked together, in the multi-segment mbufs approach. Thus,
dp_packet_resize__() has been modified to handle the DPBUF_DPDK case and
allocate and link new mbufs together as needed.

Signed-off-by: Tiago Lam <tiago.lam at intel.com>
---
 lib/dp-packet.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 82 insertions(+), 2 deletions(-)

diff --git a/lib/dp-packet.c b/lib/dp-packet.c
index 7b603c7..6a57c3c 100644
--- a/lib/dp-packet.c
+++ b/lib/dp-packet.c
@@ -238,8 +238,86 @@ dp_packet_resize__(struct dp_packet *b, size_t new_headroom, size_t new_tailroom
 
     switch (b->source) {
     case DPBUF_DPDK:
-        OVS_NOT_REACHED();
+    {
+#ifdef DPDK_NETDEV
+        uint16_t max_data_len, nb_segs;
+        size_t miss_len;
+        size_t head_diff = 0;
+        struct rte_mbuf *mbuf, *fmbuf;
+        struct rte_mempool *mp;
+
+        if (!netdev_dpdk_is_multi_segment_mbufs_enabled()) {
+            /* XXX: Handle single mbufs case better */
+            return;
+        }
+
+        /* Calculate missing length in need of allocation */
+        if (new_headroom != dp_packet_headroom(b)) {
+            /* This is a headroom adjustment. Find out how much, if anything */
+            head_diff = new_headroom - dp_packet_headroom(b);
+
+            if (head_diff <= new_tailroom) {
+                miss_len = 0;
+            } else {
+                miss_len = head_diff - new_tailroom;
+            }
+        } else {
+            /* Otherwise this is a tailroom adjustment */
+            miss_len = new_tailroom - dp_packet_tailroom(b);
+        }
+
+        mbuf = CONST_CAST(struct rte_mbuf *, &b->mbuf);
+        /* All new allocated mbuf's max data len is the same */
+        max_data_len = mbuf->buf_len - mbuf->data_off;
+        /* Calculate # of needed mbufs to accomodate 'miss_len' */
+        nb_segs = miss_len / max_data_len;
+        if (miss_len % max_data_len) {
+            nb_segs += 1;
+        }
+
+        /* Proceed with the allocation of new mbufs */
+        mp = mbuf->pool;
+        fmbuf = mbuf;
+        mbuf = rte_pktmbuf_lastseg(mbuf);
+
+        for (int i = 0; i < nb_segs; i++) {
+            /* This takes care of initialising buf_len, data_len and other
+             * fields properly */
+            struct dp_packet *pkt = dpdk_buf_alloc(mp);
+            mbuf->next = CONST_CAST(struct rte_mbuf *, &pkt->mbuf);
+            if (!mbuf->next) {
+                /* XXX: Flag a WARN and return an error as this will likely
+                 * result in undefined behaviour */
+                free_dpdk_buf((struct dp_packet *) fmbuf);
+                fmbuf = NULL;
+                break;
+            }
 
+            fmbuf->nb_segs += 1;
+
+            mbuf = mbuf->next;
+        }
+
+        /* Deal with headroom. If 'head_diff' calculated above is different
+         * than zero (thus, positive) the 'new_headroom' requested is bigger
+         * than the currently available headroom and thus, now that the needed
+         * space and mbufs have been allocated, the data needs to be shift
+         * right.
+         * XXX: Doesn't verify or take into account that new_headroom may fall
+         * outside of an mbuf limits */
+        if (head_diff > 0) {
+            new_headroom = dp_packet_headroom(b) + head_diff;
+
+            dp_packet_shift(b, head_diff);
+        }
+
+        new_base = dp_packet_base(b);
+
+        break;
+#else
+        OVS_NOT_REACHED();
+#endif
+    }
     case DPBUF_MALLOC:
         if (new_headroom == dp_packet_headroom(b)) {
             new_base = xrealloc(dp_packet_base(b), new_allocated);
@@ -263,7 +341,9 @@ dp_packet_resize__(struct dp_packet *b, size_t new_headroom, size_t new_tailroom
         OVS_NOT_REACHED();
     }
 
-    dp_packet_set_allocated(b, new_allocated);
+    if (b->source != DPBUF_DPDK) {
+        dp_packet_set_allocated(b, new_allocated);
+    }
     dp_packet_set_base(b, new_base);
 
     new_data = (char *) new_base + new_headroom;
-- 
2.7.4



More information about the dev mailing list