diff mbox series

[v13,05/24] iov_iter: skip copy if src == dst for direct data placement

Message ID 20230822150425.3390-6-aaptel@nvidia.com (mailing list archive)
State Changes Requested
Headers show
Series nvme-tcp receive offloads | expand

Checks

Context Check Description
netdev/tree_selection success Guessing tree name failed - patch did not apply, async

Commit Message

Aurelien Aptel Aug. 22, 2023, 3:04 p.m. UTC 
From: Ben Ben-Ishay <benishay@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@nvidia.com>
Signed-off-by: Boris Pismenny <borisp@nvidia.com>
Signed-off-by: Or Gerlitz <ogerlitz@nvidia.com>
Signed-off-by: Yoray Zack <yorayz@nvidia.com>
Signed-off-by: Shai Malin <smalin@nvidia.com>
Signed-off-by: Aurelien Aptel <aaptel@nvidia.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
---
 lib/iov_iter.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index e4dc809d1075..f01ee0e28295 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -313,9 +313,15 @@  size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 		return 0;
 	if (user_backed_iter(i))
 		might_fault();
+	/*
+	 * 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.
+	 */
 	iterate_and_advance(i, bytes, base, len, off,
 		copyout(base, addr + off, len),
-		memcpy(base, addr + off, len)
+		(base != addr + off) && memcpy(base, addr + off, len)
 	)
 
 	return bytes;