netdev - Re: [PATCH V7 2/4 net-next] skbuff: Add userspace zero-copy buffers in skb

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Message-Id: <20110628.163508.222352070705159851.davem@davemloft.net>
Date:	Tue, 28 Jun 2011 16:35:08 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mashirle@...ibm.com
Cc:	mst@...hat.com, eric.dumazet@...il.com, avi@...hat.com,
	arnd@...db.de, netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V7 2/4 net-next] skbuff: Add userspace zero-copy
 buffers in skb

From: Shirley Ma <mashirle@...ibm.com>
Date: Tue, 28 Jun 2011 09:51:32 -0700

> On Mon, 2011-06-27 at 15:54 -0700, David Miller wrote:
>> From: Shirley Ma <mashirle@...ibm.com>
>> Date: Mon, 27 Jun 2011 08:45:10 -0700
>> 
>> > To support skb zero-copy, a pointer is needed to add to skb share
>> info.
>> > Do you agree with this approach? If not, do you have any other
>> > suggestions?
>> 
>> I really can't form an opinion unless I am shown the complete
>> implementation, what this give us in return, what the impact is, etc. 
 ..
> You can see the overall CPU saved 50% w/i zero-copy.
> 
> The impact is every skb allocation consumed one more pointer in skb
> share info, and a pointer check in skb release when last reference is
> gone.
> 
> For skb clone, skb expand private head and skb copy, it still keeps copy
> the buffers to kernel, so we can avoid user application, like tcpdump to
> hold the user-space buffers too long.

Ok, now show me the "complete implementation".  I'm as interested in
the code as I am in the numbers, that's why I asked for both.
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