From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Durrant Subject: Re: [PATCH net v2 1/3] xen-netback: remove pointless clause from if statement Date: Fri, 28 Mar 2014 10:44:12 +0000 Message-ID: <9AAE0902D5BC7E449B7C8E4E778ABCD029E21D__49169.2944699482$1396003550$gmane$org@AMSPEX01CL01.citrite.net> References: <1395924973-42904-1-git-send-email-paul.durrant@citrix.com> <1395924973-42904-2-git-send-email-paul.durrant@citrix.com> <289461862.20140327144546@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029C992@AMSPEX01CL01.citrite.net> <68689563.20140327150256@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029CAA6@AMSPEX01CL01.citrite.net> <874580615.20140327174607@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029D28D@AMSPEX01CL01.citrite.net> <636041055.20140327181524@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029D498@AMSPEX01CL01.citrite.net> <1279623918.20140327193454@eikelenboom.it> <602920213.20140327202235@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029DDEA@AMSPEX01CL01.citrite.net> <1144281350.20140328103919@eikelenboom.it> <9AAE0902D5BC7E449B7C8E4E778ABCD029DFE7@AMSPEX01CL01.citrite.net> <063D6719AE5E284EB5DD2968C1650D6D0F6EB615@AcuExch.aculab.com> <9AAE0902D5BC7E449B7C8E4E778ABCD029E138@AMSPEX01CL01.citrite.net> <063D6719AE5E284EB5DD2968C1650D6D0F6EB72D@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D0F6EB72D@AcuExch.aculab.com> Content-Language: en-US List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: David Laight , Sander Eikelenboom Cc: "netdev@vger.kernel.org" , Wei Liu , Ian Campbell , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org > -----Original Message----- > From: David Laight [mailto:David.Laight@ACULAB.COM] > Sent: 28 March 2014 10:36 > To: Paul Durrant; Sander Eikelenboom > Cc: netdev@vger.kernel.org; Wei Liu; Ian Campbell; xen-devel@lists.xen.org > Subject: RE: [Xen-devel] [PATCH net v2 1/3] xen-netback: remove pointless > clause from if statement > > From: Paul Durrant > > > A reasonable high estimate for the number of slots required for a specific > > > message is 'frag_count + total_size/4096'. > > > So if that are that many slots free it is definitely ok to add the message. > > > > > > > Hmm, that may work. By total_size, I assume you mean skb->len, so that > calculation is based on an > > overhead of 1 non-optimally packed slot per frag. There'd still need to be a > +1 for the GSO 'extra' > > though. > > Except I meant '2 * frag_count + size/4096' :-( > And that's the pessimal estimation that's failing for Sander :-( Paul > You have to assume that every fragment starts at n*4096-1 (so need > at least two slots). A third slot is only needed for fragments > longer that 1+4096+2 - but an extra one is needed for every > 4096 bytes after that. > > David > >