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Re: [Xen-devel] RFC: [0/2] Remove netloop by lazy copying in netback

To: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir@xxxxxxxxxxxxx>, Xen Development Mailing List <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] RFC: [0/2] Remove netloop by lazy copying in netback
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Tue, 20 Mar 2007 10:22:17 +0000
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Thread-topic: [Xen-devel] RFC: [0/2] Remove netloop by lazy copying in netback
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On 20/3/07 04:46, "Herbert Xu" <herbert@xxxxxxxxxxxxxxxxxxx> wrote:

> These two patches remove the need for netloop by performing the
> copying in netback and only if it is necessary.  The rationale
> is that most packets will be processed without delay allowing
> them to be freed without copying at all.  So instead of copying
> every packet destined to dom0 we'll only copy those that linger
> longer than a specified amount of time (currently 0.5s).

One other thought I had -- does the Linux network stack ever modify date
residing outside the main skbuff data area (i.e., data in fragments)? If it
ever does, wouldn't your delayed copy in netback potentially race such
updates? If the Linux network stack guarantees never to do such a thing,
that would be nice for us. :-)

 -- Keir

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