I finally tracked down a severe performance regression on our
virtualized build servers. Before a patch and reboot cycle in late
November 2014 of the Dom0 a complete build cycle would take ~5h30,
afterwards ~9h30!

The culprit seems to be a xen update, either starting with
xen-4.2.4_02-0.7.1 (not yet verified) or xen-4.2.4_04-0.9.1 (verified
slowdown). The latest update xen-4.2.5_02-0.7.1 is also slow.
I'm currently back to normal performance with kernel-3.0.101-0.15-xen +
xen-4.2.3_08-0.7.1, which was the setup before November 2014. I first
downgraded the kernel, but that didn't change performance. Only when I
downgraded the xen packages to 4.2.3_08-0.7.1 performance came back to

The server is a dual-socket Xeon E5-2650 with 64G RAM.
Anyone experienced something similar? Did a setting/default change after