From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCH net-next] xen-netback: improve guest-receive-side flow control Date: Mon, 2 Dec 2013 11:59:30 +0000 Message-ID: <529C7622.90901@citrix.com> References: <1385644272-29728-1-git-send-email-paul.durrant@citrix.com> <529C7472.60303@citrix.com> <9AAE0902D5BC7E449B7C8E4E778ABCD019C3D2@AMSPEX01CL01.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <9AAE0902D5BC7E449B7C8E4E778ABCD019C3D2@AMSPEX01CL01.citrite.net> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Paul Durrant Cc: Wei Liu , Ian Campbell , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 02/12/13 11:55, Paul Durrant wrote: >> -----Original Message----- >> From: David Vrabel >> Sent: 02 December 2013 11:52 >> To: Paul Durrant >> Cc: xen-devel@lists.xen.org; Wei Liu; Ian Campbell >> Subject: Re: [PATCH net-next] xen-netback: improve guest-receive-side flow >> control >> >> On 28/11/13 13:11, Paul Durrant wrote: >>> The flow control code relies on a double pass of tke skb, firstly to count >>> the number of ring slots needed to supply sufficient grant references, and >>> another to actually consume those references and build the grant copy >>> operations. It transpires that, in some scenarios, the initial count and the >>> number of references consumed differs and, after this happens a number >> of >>> times, flow control is completely broken. >> >> Can you describe in more detail the cases where it gets it wrong? >> > > I've already elaborated on this thread (at Annie Li's request). That > explanation is probably a little long for inclusion in the comment though. I understand that count_slot() going wrong is bad. What specifically is it counting incorrectly. What frag layout is causing it? If this is understood there may be a more more minimal patch we can mark for stable. David