linux-kernel - Re: [PATCH net-next 1/2] ipv4: replace ip_hdr() with skb->data for optimization

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Message-ID: <CALOAHbDLJjy-1s7Tyzwuc4WDz5qtqmoZRcKptj-7efo1E-22Vg@mail.gmail.com>
Date:   Tue, 5 Jun 2018 20:29:05 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 1/2] ipv4: replace ip_hdr() with skb->data for optimization

On Tue, Jun 5, 2018 at 8:20 PM, Paolo Abeni <pabeni@...hat.com> wrote:
> On Tue, 2018-06-05 at 08:04 -0400, Yafang Shao wrote:
>> In ip receive path, when ip header hasn't been pulled yet, ip_hdr() and
>> skb->data are pointing to the same byte.
>>
>> In ip output path, when ip header is just pushed, ip_hdr() and skb->data
>> are pointing to the same byte.
>>
>> As ip_hdr() is more expensive than using skb->data, so replace ip_hdr()
>> with skb->data in these situations for optimization.
>
> IMHO this makes the code less readable and more error prone. Which kind
> of performance improvement do you measure here?
>

Correct the cc list.

Hi Paolo,

There's a "+" opertaion in ip_hdr(),  using skb->data and avoid this operation.

Thanks
Yafang