Ok, thanks for the explanation. I knew about missing SIE from one of the SHARE presentations but I didn't know that the performance downgrade will be so huge. I will try to get a free LPAR just for KVM at some point but for now I will keep learning and exploring its features in z/vm. So far I really like it. Installation was a breeze ... besides the fact that I needed to get and install demo of SLES because Red Hat is again was one step behind. As long as KVM can get close to z/vm performance then I see a great potential in it.
Gregory P 2015-09-23 15:43 GMT-04:00 Neale Ferguson <ne...@sinenomine.net>: > 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/ > ---------------------------------------------------------------------- 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/
