linux-kernel - Re: [PATCH] net: exit immediately when off = 0 in skb_headers_offset

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Message-ID: <CANn89iJ7orDEWxdBJVYqhk+1WF2ZuRpzN_XOaPoGRrn2hWjGNQ@mail.gmail.com>
Date:   Thu, 27 Aug 2020 04:37:08 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Pravin B Shelar <pshelar@....org>,
        Florian Westphal <fw@...len.de>, martin.varghese@...ia.com,
        Davide Caratti <dcaratti@...hat.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Paolo Abeni <pabeni@...hat.com>, shmulik@...anetworks.com,
        kyk.segfault@...il.com, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: exit immediately when off = 0 in skb_headers_offset_update()

On Thu, Aug 27, 2020 at 4:25 AM Miaohe Lin <linmiaohe@...wei.com> wrote:
>
> In the case of off = 0, skb_headers_offset_update() do nothing indeed.
>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  net/core/skbuff.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 18ed56316e56..f67f0da20a5b 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1459,6 +1459,8 @@ EXPORT_SYMBOL(skb_clone);
>
>  void skb_headers_offset_update(struct sk_buff *skb, int off)
>  {
> +       if (unlikely(off == 0))
> +               return;

If this is unlikely, I doubt adding a test is going to save anything.

This will instead add a conditional test for the 'likely' cases.