linux-kernel - Re: [PATCH net-next] tcp: Fix tcp_syn_flood_action() if CONFIG

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Date:   Wed, 16 Nov 2022 14:15:19 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jamie Bainbridge <jamie.bainbridge@...il.com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Chris Down <chris@...isdown.name>,
        Stephen Hemminger <stephen@...workplumber.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] tcp: Fix tcp_syn_flood_action() if
 CONFIG_IPV6=n

On Thu, 17 Nov 2022 08:39:43 +1100 Jamie Bainbridge wrote:
> >         if (v6) {
> > #ifdef v6
> >                 expensive_call6();
> > #endif
> >         } else {
> >                 expensive_call6();
> >         }  
> 
> These should work, but I expect they cause a comparison which can't be
> optimised out at compile time. This is probably why the first style
> exists.
> 
> In this SYN flood codepath optimisation doesn't matter because we're
> doing ratelimited logging anyway. But if we're breaking with existing
> style, then wouldn't the others also have to change to this style? I
> haven't reviewed all the other usage to tell if they're in an oft-used
> fastpath where such a thing might matter.

I think the word style already implies subjectivity.