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[Xen-users] qemu-dm & strange disk access


I'm running what I believe to be a PV Linux-3.1 domU (on a Linux-3.1 dom0).

I'm getting strange patterns of disk access accompanied by short lock-ups.  
Specifically, the disk will seek audibly 3 to 4 times a second, for a period 
ranging from 20 seconds to several minutes.  There will be short durations in 
these period where my SSH session is not responsive to keystrokes.  When I do:

        $ top -d .5

on dom0, I see kjournald, some other disk flushing daemon, and qemu-dm.  There 
is nothing interesting on the domU (other than whatever is running--whether 
it's the shell, or ./configure, or cc).

Seeing qemu-dm in dom0 surprises me, because I thought I was running a PV domU, 
and I'm under the impression that qemu-dm is strictly for HVM domUs.  My setup:

        * Linux-3.1 / 64-bit-only dom0 (no 32-bit glibc or toolchain)
        * Linux-3.1 / 64-bit-only domU

So my questions are (which I think are related to this issue):

        * Does anyone have an idea about the strange disk access + brief lockup?
        * What, exactly, determines a PV guest from an HVM guest?
        * Is IOMMU relevant when the Intel virtualization is disabled in BIOS?
        * Do PV guests require any PCI support *XEN_PCI*, *PCI_XEN* in either 
        * Do PV guests require PVHVM in either kernel?

I'd be happy for any insights which may narrow my search...


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