netdev - Re: [PATCH net-next v2 10/10] amd-xgbe: Rework the Rx path SKB allocation

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Message-ID: <550B3780.4080302@amd.com>
Date:	Thu, 19 Mar 2015 15:54:24 -0500
From:	Tom Lendacky <thomas.lendacky@....com>
To:	David Miller <davem@...emloft.net>
CC:	<netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 10/10] amd-xgbe: Rework the Rx path SKB allocation

On 03/19/2015 03:20 PM, David Miller wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> Date: Thu, 19 Mar 2015 15:09:08 -0500
>
>> When the driver creates an SKB it currently only copies the header
>> buffer data (which can be just the header if split header processing
>> succeeded or header plus data if split header processing did not
>> succeed) into the SKB. The receive buffer data is always added as a
>> frag, even if it could fit in the SKB. As part of SKB creation, inline
>> the receive buffer data if it will fit in the the SKB, otherwise add it
>> as a frag during SKB creation.
>>
>> Also, Update the code to trigger off of the first/last descriptor
>> indicators and remove the incomplete indicator.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>
> I do not understand the motivation for this, could you explain?
>
> The less copying you do the better, just having the headers in the
> linear area is the most optimal situation, and have all the data
> in page frag references.
>

I was trying to make the Rx path more logical from a first / last
descriptor point of view.  If it's the first descriptor allocate the
SKB, otherwise add the data as a frag. Compared to the current code:
check for null skb pointer, allocate the SKB and if there's data left
add it as a frag.

I could keep the first / last descriptor methodology and in the
xgbe_create_skb routine avoid the second copy and just always add the
other buffer as a frag. That will eliminate the extra copying. Would
that be ok or would you prefer that I just drop this patch?

Thanks,
Tom
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