Hi all, i just stumbled over a strange performance issue with my Xen setup. I use centos-virt Xen since a long time on my workstation and usually never check performance. However, yesterday I booted into the 3.18.25-19 Dom0 kernel *without* Xen and found the system noticably more responsive. That triggered me into running a simple kernel compile benchmark and compare the results: Testsequence: echo 3 > /proc/sys/vm/drop_caches make distclean cp ../.config . #copies an existing valid config for compile make oldconfig time make -j <threads> bzImage Results: xen 4.6.1 - kernel 3.18.25-19 16 threads: real 1m41.983s user 16m37.247s sys 5m7.121s 32 threads: real 1m29.240s user 23m7.170s sys 6m31.497s kernel 3.18.25-19 16 threads: real 1m12.909s user 14m37.627s sys 1m36.521s 32 threads: real 1m0.530s user 18m45.569s sys 1m58.807s Some notes: - System is a HP z840 with 2*8core E5 v3 Xeon and 128gig Ram. Disk is an Intel 750 ssd (PCIe nvme) - While normally in Xen, I limit Dom0 Memory via dom0_mem, but for the tests, Dom0 was allowed to use full memory - While running the test, no guest was running except Dom0. System was booted to graphical desktop and was completely unloaded otherwise - (boot-)logs showed no issues with ACPI or hardware-support or whatsoever. I have not yet run any in-depth investigation or tried too many different settings, but I find the differences quite noteworthy. So, if anybody came across the same issues, has some hints or suggestions, feel free. I'll continue poking around and if there is interest, i'll post updates. Regards, Thomas