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Re: [Xen-devel] 3.0.4 (and earlier): skbuff_ctor() use of xen_create_con

To: "David Edmondson" <dme@xxxxxxx>
Subject: Re: [Xen-devel] 3.0.4 (and earlier): skbuff_ctor() use of xen_create_contiguous_region()
From: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Date: Fri, 09 Mar 2007 12:45:27 +0000
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>>> David Edmondson <dme@xxxxxxx> 09.03.07 13:37 >>>
>On Fri, Mar 09, 2007 at 12:17:39PM +0000, Jan Beulich wrote:
>> While I realize that this is gone from -unstable, I'd still like to
>> understand what the purpose of using xen_create_contiguous_region()
>> in skbuff_ctor() was, and specifically what consequences I am to
>> expect when this call fails.
>So that a multi-page packet is physically contiguous when passed to
>the NIC for transmit?
>If it's not physically contiguous and the NIC hardware can't do
>scatter gather then the driver has to re-allocate and copy.

I understand that, but what I wanted clarification on is whether this is
only for performance, not for correctness (and performance would still
suffer if the allocation turns out to be beyond the physical reach of the
particular NIC).


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