On 23.09.2015 15:32, Grzegorz Powiedziuk 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”.
Although KVM should generally be run in LPAR a slowdown in an order of
magnitude in z/VM seems a bit odd.
I actually do run KVM under z/VM at my own risk (I am absolutely NOT
suggesting to do that). To recreate your problems I started a CPU
burning task in a KVM guest (stress -n 1) and see the following in the host:
Tasks: 162 total, 1 running, 161 sleeping, 0 stopped, 0 zombie
%Cpu(s): 32,5 us, 0,7 sy, 0,0 ni, 63,8 id, 0,0 wa, 0,0 hi, 0,1 si,
2,9 st
KiB Mem: 812852 total, 801232 used, 11620 free, 3152 buffers
KiB Swap: 7212140 total, 1789268 used, 5422872 free, 611460 cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+
COMMAND
38763 qemu 20 0 2842280 353068 350952 S 94,8 43,4 58:46.16
qemu-system-s39
As you can see it's less than 3% steal time in the host with roughly 95%
problem state CPU utilization for the guest process (which indicates
that SIE isn't too bad even for a 3rd level guest).
The high steal time you observe could be a hint for either z/VM swapping
on behalf of the KVM host or KVM swapping itself. Could you observe a
high page rate?
--
Mit freundlichen Grüßen/Kind Regards
Viktor Mihajlovski
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Martina Köderitz
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen
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