Where does system load live for xen related tasks? If a packet is received by dom0, then bridged into dom1, how is the system load proportioned between domains for the actual transfer of data between the two domains? I guess what I''m asking is, is there a way to report the amount of cpu time is spent in xen itself and the corresponding system load? It would be nice to be able to see the load on the physical server as a whole for monitoring purposes, or is it sufficient to simply sum up the load on all the domains? James ------------------------------------------------------- This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170 Project Admins to receive an Apple iPod Mini FREE for your judgement on who ports your project to Linux PPC the best. Sponsored by IBM. Deadline: Sept. 13. Go here: http://sf.net/ppc_contest.php _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel
> Where does system load live for xen related tasks? > If a packet is received by dom0, then bridged into dom1, how is the > system load proportioned between domains for the actual transfer of data > between the two domains? > > I guess what I''m asking is, is there a way to report the amount of cpu > time is spent in xen itself and the corresponding system load? It would > be nice to be able to see the load on the physical server as a whole for > monitoring purposes, or is it sufficient to simply sum up the load on > all the domains?Very little time will be spent in Xen, as all the hard work is done within guest context. However, the load reported by domains is currently incorrect when they are preempted --- the domain will think that whatever was running at the time it got preempted ran for the entire time that in fact someone else was running. :-( We have some ideas for how to fix this, but in fact what you really need is for Xen to record load stats on each CPU (who ran for how much on each one) and report that to control software. That also shouldn''t be too hard to add. -- Keir ------------------------------------------------------- This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170 Project Admins to receive an Apple iPod Mini FREE for your judgement on who ports your project to Linux PPC the best. Sponsored by IBM. Deadline: Sept. 13. Go here: http://sf.net/ppc_contest.php _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel
> Where does system load live for xen related tasks? > If a packet is received by dom0, then bridged into dom1, how is the > system load proportioned between domains for the actual transfer of data > between the two domains? > > I guess what I''m asking is, is there a way to report the amount of cpu > time is spent in xen itself and the corresponding system load?Very little time will be spent in Xen itself, but what there is will appear to be accounted to the domain that was running at the time. If you have a domain that is doing a lot of I/O, this will be generating work for your driver domains (usually dom0). We''ve gone to every effort to do as little work in the driver domain as possible, but it does take some CPU to execute the hardware device driver, the bridging/firewalling code, and the ''backend'' virtual driver. It''s hard to account and apportion exactly how much time the driver domain spends working on behalf of each of the other domains. If you''re worried about a domain hogging too much of this resource then use can use tools like Linux''s ''tc'' to rate limit the amount of IO a particularly domain is allowed to do.> It would be nice to be able to see the load on the physical > server as a whole for monitoring purposes, or is it sufficient > to simply sum up the load on all the domains?Xen/xend already export the information you need to sum up load over each CPU, and hence see the total system load. As Keir says, the load figures reported internally within each domain can be confused due to pre-emption. One trick we could do would be to hack Linux to create a dummy process to which we account all time when the domain isn''t running. This would enable the load figures to add up, but I''m pretty sure that this is not what many Xen users want: In a ''virtual dedicated server'' environment the owner of the physical server doesn''t want to giveq customers too much information about what else is going on on the server... Ian ------------------------------------------------------- This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170 Project Admins to receive an Apple iPod Mini FREE for your judgement on who ports your project to Linux PPC the best. Sponsored by IBM. Deadline: Sept. 13. Go here: http://sf.net/ppc_contest.php _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel
I''m only wondering from a monitoring point of view. If I have a few physical servers it will be useful to get an accurate picture of how hard each is working with a view to balancing the virtual servers sensibly across them. James> -----Original Message----- > From: Ian Pratt [mailto:Ian.Pratt@cl.cam.ac.uk] > Sent: Friday, 10 September 2004 17:32 > To: James Harper > Cc: xen-devel@lists.sourceforge.net; Ian.Pratt@cl.cam.ac.uk > Subject: Re: [Xen-devel] system load > > > Where does system load live for xen related tasks? > > If a packet is received by dom0, then bridged into dom1, how is the > > system load proportioned between domains for the actual transfer ofdata> > between the two domains? > > > > I guess what I''m asking is, is there a way to report the amount ofcpu> > time is spent in xen itself and the corresponding system load? > > Very little time will be spent in Xen itself, but what there is > will appear to be accounted to the domain that was running at the > time. > > If you have a domain that is doing a lot of I/O, this will be > generating work for your driver domains (usually dom0). We''ve > gone to every effort to do as little work in the driver domain as > possible, but it does take some CPU to execute the hardware > device driver, the bridging/firewalling code, and the ''backend'' > virtual driver. > > It''s hard to account and apportion exactly how much time the > driver domain spends working on behalf of each of the other > domains. If you''re worried about a domain hogging too much of > this resource then use can use tools like Linux''s ''tc'' to rate > limit the amount of IO a particularly domain is allowed to do. > > > It would be nice to be able to see the load on the physical > > server as a whole for monitoring purposes, or is it sufficient > > to simply sum up the load on all the domains? > > Xen/xend already export the information you need to sum up load > over each CPU, and hence see the total system load. > > As Keir says, the load figures reported internally within each > domain can be confused due to pre-emption. One trick we could do > would be to hack Linux to create a dummy process to which we > account all time when the domain isn''t running. This would enable > the load figures to add up, but I''m pretty sure that this is not > what many Xen users want: In a ''virtual dedicated server'' > environment the owner of the physical server doesn''t want to giveq > customers too much information about what else is going on on the > server... > > > Ian------------------------------------------------------- This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170 Project Admins to receive an Apple iPod Mini FREE for your judgement on who ports your project to Linux PPC the best. Sponsored by IBM. Deadline: Sept. 13. Go here: http://sf.net/ppc_contest.php _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel