netdev - Re: [PATCH V5 2/6 net-next] netdevice.h: Add zero-copy flag in netdevice

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Message-ID: <BANLkTik6aqP5BVrQNFKrnU3v=KA9ip1RoA@mail.gmail.com>
Date:	Wed, 18 May 2011 00:58:00 +0200
From:	Michał Mirosław <mirqus@...il.com>
To:	Shirley Ma <mashirle@...ibm.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Avi Kivity <avi@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 2/6 net-next] netdevice.h: Add zero-copy flag in netdevice

W dniu 18 maja 2011 00:28 użytkownik Shirley Ma <mashirle@...ibm.com> napisał:
> On Tue, 2011-05-17 at 23:48 +0200, Michał Mirosław wrote:
>> 2011/5/17 Shirley Ma <mashirle@...ibm.com>:
>> > Looks like to use a new flag requires more time/work. I am thinking
>> > whether we can just use HIGHDMA flag to enable zero-copy in macvtap
>> to
>> > avoid the new flag for now since mavctap uses real NICs as lower
>> device?
>>
>> Is there any other restriction besides requiring driver to not recycle
>> the skb? Are there any drivers that recycle TX skbs?
> Not more other restrictions, skb clone is OK. pskb_expand_head() looks
> OK to me from code review.

> Currently there is no drivers recycle TX skbs.

So why do you require the target device to have some flags at all?

Do I understand correctly, that this zero-copy feature is about
packets received from VMs?

Best Regards,
Michał Mirosław
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