linux-kernel - Re: net-scm: Macro for special pattern?

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Message-ID: <1447850630.22599.140.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 18 Nov 2015 04:43:50 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:	Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
	Julia Lawall <julia.lawall@...6.fr>
Subject: Re: net-scm: Macro for special pattern?

On Wed, 2015-11-18 at 08:45 +0100, SF Markus Elfring wrote:
> > You mean this likely() annotation of yours?
> 
> How do you think about to express the software design pattern
> which is applied at the mentioned source code place by a dedicated
> preprocessor macro?

likely()/unlikely() are not always applicable.

In the Ipv6 case I mentioned to you, it all depends if an application
for some reason absolutely wants the sockets to store the extra skb

There are seldom used socket options. _if_/_when_ they are used, a
likely()/unlikely() would give the wrong signal.

likely() should only be used in contexts we know better than branch
predictor/compiler.



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