Re: KVM got slow after adding more physical memory to host

[Avi Kivity <avi@redhat.com>]

On 09/06/2011 05:02 PM, Nikola Ciprich wrote:
> 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

How many guests in there?

Please post a trace as per http://www.linux-kvm.org/page/Tracing.

> 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

Please post /proc/mtrr and /proc/iomem.

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