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

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Message-ID: <a486bad2-917d-402b-8c37-70422dbcfeb4@nvidia.com>
Date: Mon, 15 Apr 2024 17:28:12 +0300
From: Max Gurtovoy <mgurtovoy@...dia.com>
To: Aurelien Aptel <aaptel@...dia.com>, linux-nvme@...ts.infradead.org,
 netdev@...r.kernel.org, sagi@...mberg.me, hch@....de, kbusch@...nel.org,
 axboe@...com, chaitanyak@...dia.com, davem@...emloft.net, kuba@...nel.org
Cc: aurelien.aptel@...il.com, smalin@...dia.com, malin1024@...il.com,
 ogerlitz@...dia.com, yorayz@...dia.com, borisp@...dia.com,
 galshalom@...dia.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH v24 03/20] iov_iter: skip copy if src == dst for direct
 data placement



On 04/04/2024 15:37, Aurelien Aptel wrote:
> From: Ben Ben-Ishay <benishay@...dia.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@...dia.com>
> Signed-off-by: Boris Pismenny <borisp@...dia.com>
> Signed-off-by: Or Gerlitz <ogerlitz@...dia.com>
> Signed-off-by: Yoray Zack <yorayz@...dia.com>
> Signed-off-by: Shai Malin <smalin@...dia.com>
> Signed-off-by: Aurelien Aptel <aaptel@...dia.com>
> Reviewed-by: Chaitanya Kulkarni <kch@...dia.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;
>   }
>   

Looks good,
Reviewed-by: Max Gurtovoy <mgurtovoy@...dia.com>