net/mlx5e: RX, Make sure packet header does not cross page boundary

In the non-linear SKB memory scheme of Striding RQ, a packet header
could cross page boundary. This requires special care in fast path
that costs LoC, additional runtime instructions and branches.

It could happen when the header (up to 256B) does not fit in
a single stride. Avoid this by working with a stride size that fits
the maximum possible header. Stride is increased form 64B to 256B.

Performance:
Tested packet rate for UDP streams, single ring, on ConnectX-5.

Configuration:
Set Striding RQ and LRO ON (to enabled the non-linear SKB scheme).
GRO OFF, early drop by TC rule.

64B: 4x worse memory utilization, no page-crossers headers
- No degradation (5,887,305 pps).
- The reduction in memory utilization is compensated by the saving of
  branches tests.

192B: 1.33x worse memory utilization, avoid page-crossers headers
- Before: 5,727,252. After: 5,777,037. ~1% gain.

256B: Same memory util, no page-crossers
- Before: 5,691,885. After: 5,748,007. ~1% gain.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

1 files changed, 4 insertions, 23 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index f86e4804e83e..c02532254411 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -369,7 +369,7 @@ mlx5e_add_skb_frag(struct mlx5e_rq *rq, struct sk_buff *skb,
 static inline void
 mlx5e_copy_skb_header(struct device *pdev, struct sk_buff *skb,
 		      struct mlx5e_dma_info *dma_info,
-		      int offset_from, int offset_to, u32 headlen)
+		      int offset_from, u32 headlen)
 {
 	const void *from = page_address(dma_info->page) + offset_from;
 	/* Aligning len to sizeof(long) optimizes memcpy performance */
@@ -377,24 +377,7 @@ mlx5e_copy_skb_header(struct device *pdev, struct sk_buff *skb,
 
 	dma_sync_single_for_cpu(pdev, dma_info->addr + offset_from, len,
 				DMA_FROM_DEVICE);
-	skb_copy_to_linear_data_offset(skb, offset_to, from, len);
-}
-
-static inline void
-mlx5e_copy_skb_header_mpwqe(struct device *pdev,
-			    struct sk_buff *skb,
-			    struct mlx5e_dma_info *dma_info,
-			    u32 offset, u32 headlen)
-{
-	u16 headlen_pg = min_t(u32, headlen, PAGE_SIZE - offset);
-
-	mlx5e_copy_skb_header(pdev, skb, dma_info, offset, 0, headlen_pg);
-
-	if (unlikely(offset + headlen > PAGE_SIZE)) {
-		dma_info++;
-		mlx5e_copy_skb_header(pdev, skb, dma_info, 0, headlen_pg,
-				      headlen - headlen_pg);
-	}
+	skb_copy_to_linear_data(skb, from, len);
 }
 
 static void
@@ -973,8 +956,7 @@ mlx5e_skb_from_cqe_nonlinear(struct mlx5e_rq *rq, struct mlx5_cqe64 *cqe,
 	}
 
 	/* copy header */
-	mlx5e_copy_skb_header(rq->pdev, skb, head_wi->di, head_wi->offset,
-			      0, headlen);
+	mlx5e_copy_skb_header(rq->pdev, skb, head_wi->di, head_wi->offset, headlen);
 	/* skb linear part was allocated with headlen and aligned to long */
 	skb->tail += headlen;
 	skb->len  += headlen;
@@ -1096,8 +1078,7 @@ mlx5e_skb_from_cqe_mpwrq_nonlinear(struct mlx5e_rq *rq, struct mlx5e_mpw_info *w
 		di++;
 	}
 	/* copy header */
-	mlx5e_copy_skb_header_mpwqe(rq->pdev, skb, head_di,
-				    head_offset, headlen);
+	mlx5e_copy_skb_header(rq->pdev, skb, head_di, head_offset, headlen);
 	/* skb linear part was allocated with headlen and aligned to long */
 	skb->tail += headlen;
 	skb->len  += headlen;