[dpdk-dev] [RFC PATCH] ixgbe: ixgbe_recv_pkts_vec shouldn't override mbuf buffer length

[Konstantin Ananyev]

That's an alternative way to fix the problem described in the patch:
http://dpdk.org/ml/archives/dev/2014-December/009394.html.
The main difference is:
- move buf_len fields out of rearm_data marker.
- make ixgbe_recv_pkts_vec() not touch buf_len field at all
(as all other RX functions behave).

Signed-off-by: Konstantin Ananyev <konstantin.ananyev at intel.com>
---
 lib/librte_mbuf/rte_mbuf.h            |  7 +++++--
 lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c | 20 +++++++++++++++-----
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 2e5fce5..bb88318 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -179,6 +179,8 @@ const char *rte_get_tx_ol_flag_name(uint64_t mask);
 typedef void    *MARKER[0];   /**< generic marker for a point in a structure */
 typedef uint64_t MARKER64[0]; /**< marker that allows us to overwrite 8 bytes
                                * with a single assignment */
+typedef uint8_t MARKER8[0];   /**< generic marker with 1B alignment */
+
 /**
  * The generic rte_mbuf, containing a packet mbuf.
  */
@@ -188,9 +190,10 @@ struct rte_mbuf {
        void *buf_addr;           /**< Virtual address of segment buffer. */
        phys_addr_t buf_physaddr; /**< Physical address of segment buffer. */

-       /* next 8 bytes are initialised on RX descriptor rearm */
-       MARKER64 rearm_data;
        uint16_t buf_len;         /**< Length of segment buffer. */
+
+       /* next 6 bytes are initialised on RX descriptor rearm */
+       MARKER8 rearm_data;
        uint16_t data_off;

        /**
diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c 
b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
index 579bc46..d5fc0cc 100644
--- a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
+++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
@@ -79,13 +79,22 @@ ixgbe_rxq_rearm(struct igb_rx_queue *rxq)
        /* Initialize the mbufs in vector, process 2 mbufs in one loop */
        for (i = 0; i < RTE_IXGBE_RXQ_REARM_THRESH; i += 2, rxep += 2) {
                __m128i vaddr0, vaddr1;
+               uintptr_t p0, p1;

                mb0 = rxep[0].mbuf;
                mb1 = rxep[1].mbuf;

-               /* flush mbuf with pkt template */
-               mb0->rearm_data[0] = rxq->mbuf_initializer;
-               mb1->rearm_data[0] = rxq->mbuf_initializer;
+               /*
+                * Flush mbuf with pkt template.
+                * Data to be rearmed is 6 bytes long.
+                * Though, RX will overwrite ol_flags that are coming next
+                * anyway. So overwrite whole 8 bytes with one load:
+                * 6 bytes of rearm_data plus first 2 bytes of ol_flags.
+                */
+               p0 = (uintptr_t)&mb0->rearm_data;
+               *(uint64_t *)p0 = rxq->mbuf_initializer;
+               p1 = (uintptr_t)&mb1->rearm_data;
+               *(uint64_t *)p1 = rxq->mbuf_initializer;

                /* load buf_addr(lo 64bit) and buf_physaddr(hi 64bit) */
                vaddr0 = _mm_loadu_si128((__m128i *)&(mb0->buf_addr));
@@ -732,14 +741,15 @@ static struct ixgbe_txq_ops vec_txq_ops = {
 int
 ixgbe_rxq_vec_setup(struct igb_rx_queue *rxq)
 {
+       uintptr_t p;
        struct rte_mbuf mb_def = { .buf_addr = 0 }; /* zeroed mbuf */

        mb_def.nb_segs = 1;
        mb_def.data_off = RTE_PKTMBUF_HEADROOM;
-       mb_def.buf_len = rxq->mb_pool->elt_size - sizeof(struct rte_mbuf);
        mb_def.port = rxq->port_id;
        rte_mbuf_refcnt_set(&mb_def, 1);
-       rxq->mbuf_initializer = *((uint64_t *)&mb_def.rearm_data);
+       p = (uintptr_t)&mb_def.rearm_data;
+       rxq->mbuf_initializer = *(uint64_t *)p;
        return 0;
 }

-- 
1.8.3.1