netdev - Re: [PATCH net-next] net: reorganize sk_buff for faster __copy_skb

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Date:	Fri, 26 Sep 2014 10:35:32 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Amir Vadai <amirv@...lanox.com>,
	John Fastabend <john.r.fastabend@...el.com>, brouer@...hat.com
Subject: Re: [PATCH net-next] net: reorganize sk_buff for faster
 __copy_skb_header()

On Thu, 25 Sep 2014 14:20:04 -0700
Eric Dumazet <eric.dumazet@...il.com> wrote:

> From: Eric Dumazet <edumazet@...gle.com>
> 
> With proliferation of bit fields in sk_buff, __copy_skb_header() became
> quite expensive, showing as the most expensive function in a GSO
> workload.
> 
> __copy_skb_header() performance is also critical for non GSO TCP
> operations, as it is used from skb_clone()
> 
> This patch carefully moves all the fields that were not copied in a
> separate zone : cloned, nohdr, fclone, peeked, head_frag, xmit_more
> 
> Then I moved all other fields and all other copied fields in a section
> delimited by headers_start[0]/headers_end[0] section so that we
> can use a single memcpy() call, inlined by compiler using long
> word load/stores.
> 
> I also tried to make all copies in the natural orders of sk_buff,
> to help hardware prefetching.
> 
> I made sure sk_buff size did not change.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---

I'm impressed, network ninja!

Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>

It would have been nice if you would have included the performance
improvement you saw, e.g. from:
 http://thread.gmane.org/gmane.linux.network/332035/focus=332086

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer
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