[PATCH v12 05/26] iov_iter: skip copy if src == dst for direct data placement
Max Gurtovoy
mgurtovoy at nvidia.com
Tue Aug 15 17:24:14 PDT 2023
On 12/07/2023 19:14, Aurelien Aptel wrote:
> 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 | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index b667b1e2f688..1c9b10e1e1c8 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;
Looks good,
Reviewed-by: Max Gurtovoy <mgurtovoy at nvidia.com>
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