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

From: Tom Lendacky <[email-masked]>
Date: Thu, 19 Mar 2015 15:54:24 -0500

On 03/19/2015 03:20 PM, David Miller wrote:
> From: Tom Lendacky <[email-masked]>
> 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 <[email-masked]>
>
> 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