net: hns3: support dma_map_sg() for multi frags skb

Using the queue based tx buffer, it is also possible to allocate a
sgl buffer, and use skb_to_sgvec() to convert the skb to the sgvec
in order to support the dma_map_sg() to decreases the overhead of
IOMMU mapping and unmapping.

Firstly, it reduces the number of buffers. For example, a tcp skb
may have a 66-byte header and 3 fragments of 4328, 32768, and 28064
bytes. With this patch, dma_map_sg() will combine them into two
buffers, 66-bytes header and one 65160-bytes fragment by using IOMMU.

Secondly, it reduces the number of dma mapping and unmapping. All the
original 4 buffers are mapped only once rather than 4 times.

The throughput improves above 10% when running single thread of iperf
using TCP when IOMMU is in strict mode.

Suggested-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.h b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.h
index 8d147c1dab2c..22ae291471aa 100644
--- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.h
+++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.h
@@ -306,6 +306,7 @@ enum hns3_desc_type {
 	DESC_TYPE_PAGE			= 1 << 2,
 	DESC_TYPE_BOUNCE_ALL		= 1 << 3,
 	DESC_TYPE_BOUNCE_HEAD		= 1 << 4,
+	DESC_TYPE_SGL_SKB		= 1 << 5,
 };
 
 struct hns3_desc_cb {
@@ -410,6 +411,9 @@ struct ring_stats {
 			u64 tx_bounce;
 			u64 tx_spare_full;
 			u64 copy_bits_err;
+			u64 tx_sgl;
+			u64 skb2sgl_err;
+			u64 map_sg_err;
 		};
 		struct {
 			u64 rx_pkts;