From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: xennet: skb rides the rocket: 20 slots Date: Tue, 8 Jan 2013 10:05:49 +0000 Message-ID: <1357639549.7989.147.camel@zakaz.uk.xensource.com> References: <72958707.20130104172854@eikelenboom.it> <1357556115.7989.13.camel@zakaz.uk.xensource.com> <50EB8091.90705@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <50EB8091.90705@oracle.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: ANNIE LI Cc: Sander Eikelenboom , Konrad Rzeszutek Wilk , xen-devel List-Id: xen-devel@lists.xenproject.org On Tue, 2013-01-08 at 02:12 +0000, ANNIE LI wrote: > >> > >> I have added some extra info, but i don't have enough knowledge if > >> this could/should be prevented from happening ? > > MAX_SKB_FRAGS has never, AFAIK, been as big as 19 or 20 so I'm not sure > > this can have ever worked. > > > > These SKBs seem to be pretty big (not quite 64KB), seemingly most of the > > data is contained in a smallish number of frags, which suggests compound > > pages and therefore a reasonably modern kernel? > > > > This probably relates somewhat to the issues described in the > > "netchannel vs MAX_SKB_FRAGS" thread last year, or at least the solution > > to that would necessarily involve fixing this issue. > > If netback complains about "Too many frags", then it should be > MAX_SKB_FRAGS limitation in netback results in dropping packets in > netfront. It is possible that other netfronts(windows?) also hit this. It's very possible. I rather suspect that non-Linux frontends have workarounds (e.g. manual resegmenting etc) for this case. Ian.