netdev - Re: [PATCH net-next v5 1/3] net: ipv6: Unduplicate {raw,udp}v6

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Date:	Fri, 25 Apr 2014 23:26:42 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Miller <davem@...emloft.net>
Cc:	David.Laight@...LAB.COM, lorenzo@...gle.com,
	netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org,
	eric.dumazet@...il.com
Subject: Re: [PATCH net-next v5 1/3] net: ipv6: Unduplicate {raw,udp}v6_sendmsg code

On Fri, Apr 25, 2014 at 01:33:03PM -0400, David Miller wrote:
> From: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Date: Fri, 25 Apr 2014 19:19:09 +0200
> 
> > Maybe we can put all those hlimit, tclass, dontfrag vars into a struct
> > and just pass one pointer.
> 
> It's still an unnecessary memory dereference.

True, true.

> The compiler can potentially optimize the accesses to those variables
> into a local register with the existing code, with this consolidation
> it no longer can.

We could hack up the function in a local header file in net/ipv6 and
__always_inline it. If the resulting assembly looks good would this
be acceptable for you? Maybe we could switch to something like struct
ipv6_output_opts where we gather all those state variables common to
the code paths.

Thanks,

  Hannes

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