netdev - Re: [PATCH RFC 00/14] shrink skb cb to 44 bytes

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Message-ID: <1425333400.5130.136.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 02 Mar 2015 13:56:40 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Florian Westphal <fw@...len.de>
Cc:	netdev@...r.kernel.org, Johannes Berg <johannes@...solutions.net>,
	linux-wireless@...r.kernel.org
Subject: Re: [PATCH RFC 00/14] shrink skb cb to 44 bytes

On Mon, 2015-03-02 at 21:42 +0100, Florian Westphal wrote:

> Thats right.  Do you think its worth to already move cb[] near the end
> of skb and alter build_skb to not clear it anymore?
> 
> Which of the ideas, in your opinion, is worth pursuing first (if any)?

moving cb[] near the end will void my patches to use one cache line per
skb in TCP receive queue ( or write queue)

971f10eca186ca tcp: better TCP_SKB_CB layout to reduce cache line misses


I have worked a bit (3 months ago) about doing the skb->cb[] selective
clearing, but a lot of alloc_skb() users _assume_ it is already
cleared. 

That seemed a lot of work to me, because of the many alloc_skb()
variants we have. But definitely worth trying to complete.



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