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

Gleb Natapov
2011-09-06T16:11:08Z

On Tue, Sep 06, 2011 at 07:06:34PM +0300, Avi Kivity wrote:
> On 09/06/2011 07:01 PM, Nikola Ciprich wrote:
> >> 404
> >ouch, dumb me :-/
> >http://nelide.cz/downloads/nik/trace.dat.bz2
> >sorry
> >n.
> >
>
> qemu-kvm-4618 [000] 13698.803169: kvm_emulate_insn:
> 0:806edb12: rep outsw
> qemu-kvm-4618 [000] 13698.803170: kvm_pio:
> pio_write at 0x1f0 size 2 count 1
> qemu-kvm-4618 [000] 13698.803171: kvm_userspace_exit:
> reason KVM_EXIT_IO (2)
> qemu-kvm-4618 [000] 13698.803186: kvm_entry: vcpu 0
> qemu-kvm-4618 [000] 13698.803189: kvm_exit:
> reason IO_INSTRUCTION rip 0x806edb12 info 1f00031 0
>
> qemu-kvm-4618 [000] 13698.803191: kvm_emulate_insn:
> 0:806edb12: rep outsw
> qemu-kvm-4618 [000] 13698.803192: kvm_pio:
> pio_write at 0x1f0 size 2 count 1
> qemu-kvm-4618 [000] 13698.803193: kvm_userspace_exit:
> reason KVM_EXIT_IO (2)
> qemu-kvm-4618 [000] 13698.803195: kvm_entry: vcpu 0
> qemu-kvm-4618 [000] 13698.803198: kvm_exit:
> reason IO_INSTRUCTION rip 0x806edb12 info 1f00031 0
>
>
> One of your guests is using IDE PIO instead of DMA. Switch it back to DMA.
>
> Gleb, is rep/outsw our pio regression or was it another instruction?
>
It is rep/in-out. But why it became noticeable only after adding more
physical memory to the host is a mystery.

--
Gleb.