netdev - Re: [net-next PATCH v3 4/6] udp: Partially unroll handling of first segment and last segment

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Date:   Mon, 7 May 2018 12:59:28 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [net-next PATCH v3 4/6] udp: Partially unroll handling of first
 segment and last segment

On Mon, May 7, 2018 at 12:54 PM, Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
> On Mon, May 7, 2018 at 2:57 PM, Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
>> On Mon, May 7, 2018 at 2:08 PM, Alexander Duyck
>> <alexander.duyck@...il.com> wrote:
>>> From: Alexander Duyck <alexander.h.duyck@...el.com>
>>>
>>> This patch allows us to take care of unrolling the first segment and the
>>> last segment of the loop for processing the segmented skb. Part of the
>>> motivation for this is that it makes it easier to process the fact that the
>>> first fame and all of the frames in between should be mostly identical
>>> in terms of header data, and the last frame has differences in the length
>>> and partial checksum.
>>>
>>> In addition I am dropping the header length calculation since we don't
>>> really need it for anything but the last frame and it can be easily
>>> obtained by just pulling the data_len and offset of tail from the transport
>>> header.
>>>
>>> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
>>
>> I'm not a fan of the more complicated control flow, as I pointed out
>> before. It only seems to save one assignment to uh from segs.
>>
>> Both follow-up patches are now more complex, because they need
>> to add the same code in two locations.
>
> With that said, if you feel strongly, I don't object.
>
> The removal of hdrlen and simplification of arguments is definitely
> an improvement.

Thanks for being understanding about this.

My preference is to keep the loop unrolled as it is since that way it
is not too different from the way we handle this for TCP so it will
maintenance of the two easier. Otherwise I have to add a bunch of
conditional checks inside the loop.

The other advantage to unrolling it as I did is that I don't have to
deal with a ton of extra indentation for an if statement inside of a
while loop.

- Alex