[PATCH v24 03/20] iov_iter: skip copy if src == dst for direct data placement

[Aurelien Aptel]

From: Ben Ben-Ishay <benishay at nvidia.com>

When using direct data placement (DDP) the NIC could write the payload
directly into the destination buffer and constructs SKBs such that
they point to this data. To skip copies when SKB data already resides
in the destination buffer we check if (src == dst), and skip the copy
when it's true.

Signed-off-by: Ben Ben-Ishay <benishay at nvidia.com>
Signed-off-by: Boris Pismenny <borisp at nvidia.com>
Signed-off-by: Or Gerlitz <ogerlitz at nvidia.com>
Signed-off-by: Yoray Zack <yorayz at nvidia.com>
Signed-off-by: Shai Malin <smalin at nvidia.com>
Signed-off-by: Aurelien Aptel <aaptel at nvidia.com>
Reviewed-by: Chaitanya Kulkarni <kch at nvidia.com>
---
 lib/iov_iter.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 4a6a9f419bd7..a85125485174 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -62,7 +62,14 @@ static __always_inline
 size_t memcpy_to_iter(void *iter_to, size_t progress,
 		      size_t len, void *from, void *priv2)
 {
-	memcpy(iter_to, from + progress, len);
+	/*
+	 * When using direct data placement (DDP) the hardware writes
+	 * data directly to the destination buffer, and constructs
+	 * IOVs such that they point to this data.
+	 * Thus, when the src == dst we skip the memcpy.
+	 */
+	if (iter_to != from + progress)
+		memcpy(iter_to, from + progress, len);
 	return 0;
 }
 
-- 
2.34.1