From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: 3.0.4 (and earlier): skbuff_ctor() use of xen_create_contiguous_region() Date: Fri, 09 Mar 2007 12:45:27 +0000 Message-ID: <45F164F7.76E4.0078.0@novell.com> References: <45F15E73.76E4.0078.0@novell.com> <20070309123724.GQ25301@cheesecake.uk.sun.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20070309123724.GQ25301@cheesecake.uk.sun.com> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: David Edmondson Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org >>> David Edmondson 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). Jan