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

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Date:   Tue, 05 Jun 2018 14:20:42 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Yafang Shao <laoar.shao@...il.com>, edumazet@...gle.com,
        davem@...emloft.net
Cc:     netdev@...r.kernel.org, inux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] ipv4: replace ip_hdr() with skb->data for
 optimization

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?

Thanks,

Paolo