netdev - RE: [PATCH v15 00/17] Provide a zero-copy method on KVM virtio-net.

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Date:	Wed, 17 Nov 2010 16:09:12 +0800
From:	"Xin, Xiaohui" <xiaohui.xin@...el.com>
To:	"Xin, Xiaohui" <xiaohui.xin@...el.com>,
	David Miller <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>, "mingo@...e.hu" <mingo@...e.hu>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"jdike@...ux.intel.com" <jdike@...ux.intel.com>
Subject: RE: [PATCH v15 00/17] Provide a zero-copy method on KVM virtio-net.

>-----Original Message-----
>From: kvm-owner@...r.kernel.org [mailto:kvm-owner@...r.kernel.org] On Behalf Of Xin,
>Xiaohui
>Sent: Thursday, November 11, 2010 4:28 PM
>To: David Miller
>Cc: netdev@...r.kernel.org; kvm@...r.kernel.org; linux-kernel@...r.kernel.org;
>mst@...hat.com; mingo@...e.hu; herbert@...dor.apana.org.au; jdike@...ux.intel.com
>Subject: RE: [PATCH v15 00/17] Provide a zero-copy method on KVM virtio-net.
>
>>-----Original Message-----
>>From: David Miller [mailto:davem@...emloft.net]
>>Sent: Thursday, November 11, 2010 1:47 AM
>>To: Xin, Xiaohui
>>Cc: netdev@...r.kernel.org; kvm@...r.kernel.org; linux-kernel@...r.kernel.org;
>>mst@...hat.com; mingo@...e.hu; herbert@...dor.apana.org.au; jdike@...ux.intel.com
>>Subject: Re: [PATCH v15 00/17] Provide a zero-copy method on KVM virtio-net.
>>
>>From: xiaohui.xin@...el.com
>>Date: Wed, 10 Nov 2010 17:23:28 +0800
>>
>>> From: Xin Xiaohui <xiaohui.xin@...el.com>
>>>
>>>>2) The idea to key off of skb->dev in skb_release_data() is
>>>>   fundamentally flawed since many actions can change skb->dev on you,
>>>>   which will end up causing a leak of your external data areas.
>>>
>>> How about this one? If the destructor_arg is not a good candidate,
>>> then I have to add an apparent field in shinfo.
>>
>>If destructor_arg is actually a net_device pointer or similar,
>>you will need to take a reference count on it or similar.
>>
>Do you mean destructor_arg will be consumed by other user?
>If that case, may I add a new structure member in shinfo?
>Thus only zero-copy will use it, and no need for the reference count.
>
How about this? It really needs somewhere to track the external data area,
and if something wrong with it, we can also release the data area. We think 
skb_release_data() is the right place to deal with it. If I understood right,
that destructor_arg will be used by other else that why reference count is
needed, then how about add a new structure member in shinfo?

Thanks
Xiaohui 

>>Which means --> good bye performance especially on SMP.
>>
>>You're going to be adding new serialization points and at
>>least two new atomics per packet.
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