I think that is an interesting coincidence about x86_64 vs. 32bit kernel. In this same CentOS pv domU I was talking about I created an x86_64 by "accident." I ended up knocking it down and going to i386 tree (its a web app) and found it to be snappier. Please post your results especially if it is a kernel difference. Daniel De Marco wrote: > Ben, > > thanks for the suggestion, it didn't work, but it led me to test the > network of the domu and it turns out that with netperf to a different > machine I can get ~500Mbit/s from the domU and ~950Mbit/s from the dom0. > >>From another domU on a different dom0 (older systems, centos 5.3 with > kernel 2.6.18-92.1.22.el5xen i686 instead of 2.6.18-164.el5xen x86_64) > netperf produces 950Mbit/s as well. > > The weird thing is however that it's dom0 that acts as iSCSI initiator, > so it is dom0 that is using the network and there it works fine. > > I'll go do some more tests. > Daniel. > > > * Ben Montanelli <montanelli at rivint.com> [09/24/2009 14:45]: >> Are you using separate physical NICs for dom0 (isolated) and the domUs? >> >> In a CentOS domU I just, a few hours ago, had same issue on network >> reads, but doing: >> >> # ethtool -K eth0 tx off >> >> then rebooted domU and it cleared up and got much closer to max. Yes, >> that is the TX checksum fix, but it seemed to affect my reads (IO in). >> >> >> >> Daniel De Marco wrote: >>> Hi, >>> >>> I'm setting up xen (on centos 5.3) and I'm facing a weird performance >>> issue with iSCSI. >>> >>> I attach the iSCSI targets to dom0 and if I use them from dom0 I obtain >>> good performance with simple dd tests (~100MB/s both reading and >>> writing). >>> >>> I then use the block devices for the domU and if I repeat the same dd >>> test >>> from within the domU the write performace is still good (~100MB/s), but >>> the read performance is cut in half (~55MB/s). >>> >>> I tried changing several parameters like read_ahead and such, but I can >>> not obtain a good read performance in the domU. >>> >>> Any idea? >>> >>> Thanks, Daniel. >>> >>> _______________________________________________ >>> CentOS-virt mailing list >>> CentOS-virt at centos.org >>> http://lists.centos.org/mailman/listinfo/centos-virt >>> >> _______________________________________________ >> CentOS-virt mailing list >> CentOS-virt at centos.org >> http://lists.centos.org/mailman/listinfo/centos-virt > _______________________________________________ > CentOS-virt mailing list > CentOS-virt at centos.org > http://lists.centos.org/mailman/listinfo/centos-virt >