I am seeing a strange behaviour with Xen-3.0.4 which seems to suggest that Dom0 has either higher Scheduling affinity or Interrupt affinity. I am in the initial stages of investigation and it is possible that my hunch is totally wrong. I would like to hear comments or questions from the experts. I have a multifunction NIC card, with one function being used by Dom0 and another one exported to DomU using PCI passthrough Dom0 and DomU have almost the same memory allocated to each (~1.3G). The ports themselves are operating at the same speed and share the same IRQ. iperf (as a client) is started on Dom0 in the same way as it is started on DomU. iperf results are skewed in favour of Dom0 in the ratio 10:1. Given all other things are similar wouldn''t it be normal to expect throughputs in the ratio of 1:1. (ps:- The 2 ports on the Xen machine is connected "point-to-point-wise" to 2 ports on another machine running Linux natively) Regards, Jambunathan K. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Jambunathan K
2007-Mar-27 14:40 UTC
[Xen-devel] Re: PCI Passthrough & iperf Throughput Skew
Additional Data Point: If I just exercise iperf in Dom0 or DomU *separately*, I get identical throughput . The 10:1 skew happens only when the iperf is running concurrently on the Dom0 and DomU. Regards, Jambunathan K. Jambunathan K wrote:> I am seeing a strange behaviour with Xen-3.0.4 which seems to suggest > that Dom0 has either higher Scheduling affinity or Interrupt affinity. > > I am in the initial stages of investigation and it is possible that my > hunch is totally wrong. I would like to hear comments or questions > from the experts. > > I have a multifunction NIC card, with one function being used by Dom0 > and another one exported to DomU using PCI passthrough > > Dom0 and DomU have almost the same memory allocated to each > (~1.3G). The ports themselves are operating at the same speed and > share the same IRQ. > > iperf (as a client) is started on Dom0 in the same way as it is > started on DomU. > > iperf results are skewed in favour of Dom0 in the ratio 10:1. > > Given all other things are similar wouldn''t it be normal to expect > throughputs in the ratio of 1:1. > > (ps:- The 2 ports on the Xen machine is connected > "point-to-point-wise" to 2 ports on another machine running Linux > natively) > > > Regards, > Jambunathan K. > > > > > > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel