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

[Gleb Natapov <gleb@redhat.com>]

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.