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

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Message-ID: <F2E9EB7348B8264F86B6AB8151CE2D793498A31E75@shsmsx502.ccr.corp.intel.com>
Date:	Thu, 11 Nov 2010 16:28:21 +0800
From:	"Xin, Xiaohui" <xiaohui.xin@...el.com>
To:	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: 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.

>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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