[dpdk-dev] [PATCH v2 2/2] app/testpmd/txonly: Reset headroom after raw packet allocation

[Maxime Coquelin <maxime.coquelin@redhat.com>]

This patch fixes txonly raw packets allocations by resetting the
available headroom.

Indeed, some PMDs such as Virtio might prepend some data to the
packet, resulting in mbuf's data_off field to be decremented each
time the mbuf gets re-allocated.

For Virtio PMD, it means that we use only single descriptors for the
first times mbufs get allocated, as at some point there is not
enough headroom to store the header.

Other alternative would be use standard API to allocate the packets,
which does reset the headroom, but the impact on performance is too
big to consider this an option.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 app/test-pmd/txonly.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/app/test-pmd/txonly.c b/app/test-pmd/txonly.c
index d2736b7..8513a06 100644
--- a/app/test-pmd/txonly.c
+++ b/app/test-pmd/txonly.c
@@ -222,6 +222,14 @@ pkt_burst_transmit(struct fwd_stream *fs)
 				return;
 			break;
 		}
+
+		/*
+		 * Using raw alloc is good to improve performance,
+		 * but some consumers may use the headroom and so
+		 * decrement data_off. We need to make sure it is
+		 * reset to default value.
+		 */
+		rte_pktmbuf_reset_headroom(pkt);
 		pkt->data_len = tx_pkt_seg_lengths[0];
 		pkt_seg = pkt;
 		if (tx_pkt_split == TX_PKT_SPLIT_RND)
-- 
2.7.4