KVM under z/VM will suck because the hardware only supports two levels of “SIE”. SIE is whats used to allow an LPAR and a virtual machine to operate at hardware speeds. A lot of the stuff that used to be done by VM/SP and predecessors when running virtual machines is done by the hardware (well the microcode/millicode/…).
A virtual machine that tries to dispatch a guest of its own on SIE (like KVM running on z/VM) has to get all those operations performed by the hypervisor and not the hardware. Thus you get an enormous overhead and the performance you are experiencing. On 9/23/15, 3:32 PM, "Linux on 390 Port on behalf of Grzegorz Powiedziuk" <LINUX-390@VM.MARIST.EDU on behalf of gpowiedz...@gmail.com> wrote: >BTW, I was playing with KVM few days ago and it looks pretty awesome in >terms of maintaining the environment and deploying new VMs but the >performance for me was really bad. >And I mean extremely bad. I am not sure if it was because I made the KVM >host (sles12) run as a virtual machine in z/VM or I was doing something >else wrong. I know that having kvm virtual machines in a 3rd level (under >sles -> under z/VM) will impact performance but my case it was extremly >bad. It was like running linux in hercules s390 in 2006 on old x86 >desktop. > >The installation of linux in kvm virtual machine took 3-4 hours. Every >operation that involves cpu and memory takes 3-10 time more time than on >a KVM host itself. >Whenever something is happening in kvm virtual machine, the performance >toolkit shows that KVM host is doing about 50% in supervisor mode and 50% >in emulation mode which makes the t/v ratio for this machine about 2 >which is pretty bad. I didn’t have time to do more investigation on this >yet. >The KVM host (Server) sees about 50% cpu time as a “steal time”. ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
