Hi. We seem to be experiencing a very odd issue with Xen 3.0 (RPM version under CentOS). When establishing a socket (via any application - for example telnet to a mailserver on port 25) there is an almost precise 10 second delay before there is any throughput. This only happens intermittently and appears to occur on all VDSs on the same system. This does not occur on identical physical systems on the same network. dmesg on the host node shows lots of ''xen_net: Memory squeeze in netback driver.'' but I''m not convinced this is the cause as they do not correspond with the delays. It''s almost as if it''s waiting for something to time out... Many thanks in advance for your assistance/thoughts/ideas/input. Regards, Adam Smith. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tue, Aug 08, 2006 at 04:26:17PM +0100, Adam Smith wrote:> Hi. We seem to be experiencing a very odd issue with Xen 3.0 (RPM > version under CentOS). When establishing a socket (via any application > - for example telnet to a mailserver on port 25) there is an almost > precise 10 second delay before there is any throughput. This only > happens intermittently and appears to occur on all VDSs on the same > system. This does not occur on identical physical systems on the same > network.Whilst this could be a Xen issue have you tested things like DNS? It could be that all the services you''re attempting to connect to are timing out on doing lookups of the IPs which are connecting. (Or similarly a mailserver might be trying ident lookups.) Steve -- _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Thanks but that''s the first thing we tried. It''s not a DNS lookup causing the delay (we''re connecting by IP address) and we''ve ruled out anything on the remote server. It occurs on any port, with any service as far as we can tell. Steve Kemp wrote:> On Tue, Aug 08, 2006 at 04:26:17PM +0100, Adam Smith wrote: > > >> Hi. We seem to be experiencing a very odd issue with Xen 3.0 (RPM >> version under CentOS). When establishing a socket (via any application >> - for example telnet to a mailserver on port 25) there is an almost >> precise 10 second delay before there is any throughput. This only >> happens intermittently and appears to occur on all VDSs on the same >> system. This does not occur on identical physical systems on the same >> network. >> > > Whilst this could be a Xen issue have you tested things like > DNS? > > It could be that all the services you''re attempting to connect > to are timing out on doing lookups of the IPs which are connecting. > (Or similarly a mailserver might be trying ident lookups.) > > Steve > > ------------------------------------------------------------------------ > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users-- Adam Smith UK Webhosting Ltd. Tel (0870) 0115578 Fax (01323) 741135 http://www.2host.co.uk http://www.registron.co.uk sales@ukwebhosting.ltd.uk The above information is confidential to the addressee and may be privileged. Unauthorised access and use is prohibited. Internet communications are not secure and therefore this company does not accept legal responsibility for the contents of this message. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited and may be unlawful. UK Webhosting Ltd is registered in England and Wales, number 04977925. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
On Tue, Aug 08, 2006 at 04:53:31PM +0100, Adam Smith wrote:> Thanks but that''s the first thing we tried. It''s not a DNS lookup > causing the delay (we''re connecting by IP address) and we''ve ruled out > anything on the remote server. It occurs on any port, with any service > as far as we can tell.(For DNS I meant that the service you''re connecting to might be timing out doing lookups of the IPs it sees connecting; so even if you''re connecting to the server by IP addresses that could still be the problem. Anyway you say you''ve ruled it out, thats good enough for me.) I guess the next obvious thing to try is to disable the TCP checksumming and see if that helps. Run the following as root on the system which is having the problem(s): ethtool -K eth0 tx off See if that helps? Steve -- _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Thanks Steve but that didn''t do it either. It''s not the remote server doing an rDNS lookup as it doesn''t occur with adjacent machines on the same /24 (with the same reverse delegation). Regards, Adam. Steve Kemp wrote:> On Tue, Aug 08, 2006 at 04:53:31PM +0100, Adam Smith wrote: > > >> Thanks but that''s the first thing we tried. It''s not a DNS lookup >> causing the delay (we''re connecting by IP address) and we''ve ruled out >> anything on the remote server. It occurs on any port, with any service >> as far as we can tell. >> > > (For DNS I meant that the service you''re connecting to might be > timing out doing lookups of the IPs it sees connecting; so even > if you''re connecting to the server by IP addresses that could > still be the problem. Anyway you say you''ve ruled it out, thats > good enough for me.) > > I guess the next obvious thing to try is to disable the TCP > checksumming and see if that helps. > > Run the following as root on the system which is having the > problem(s): > > ethtool -K eth0 tx off > > See if that helps? > > Steve >-- Adam Smith UK Webhosting Ltd. Tel (0870) 0115578 Fax (01323) 741135 http://www.2host.co.uk http://www.registron.co.uk sales@ukwebhosting.ltd.uk The above information is confidential to the addressee and may be privileged. Unauthorised access and use is prohibited. Internet communications are not secure and therefore this company does not accept legal responsibility for the contents of this message. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited and may be unlawful. UK Webhosting Ltd is registered in England and Wales, number 04977925. _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users