KVM got slow after adding more physical memory to host

Nikola Ciprich
2011-09-06T14:34:53Z

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Hello,

I'm trying to solve quite a weird problem on one of our customers' box.
It's quad core Xeon X3430 @ 2.40GHz, running 64bit centos with 2.6.38 (I also tried upgrading to
2.6.39).
After increasing physical memory from 16 to 20GB, all guest got incredibly slow, starting just
one windows or linux guest causes host to be quite slow, and quest seems to be even slower.
hardware virtualisation is on, KVM is used, no relevant update since the update.
here's about 3 seconds of kvm_stat:

kvm_exit 659513 103922
kvm_entry 659505 103920
kvm_emulate_insn 631118 99344
kvm_exit(IO_INSTRUCTION) 625223 98398
kvm_userspace_exit 624979 98359
kvm_pio 624970 98357

but according to atop, there is almost no I/O activity from guests, and running top in them
shows them to really be idle...
but they eat like 60-70% of host CPU core time each..

Do You have any idea on what should I check?
thanks a lot in advance

nik
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Ing. Nikola CIPRICH
LinuxBox.cz, s.r.o.
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