[qubes-users] xentop's disk I/O

Hi!

Watching xentop, I have a question:
I know that the network operations aren't accounted in xentop when running Qubes OS, but I'm wondering:
For domain-0 all of the disk I/O (VBD_RD, VBD_WR, VBD_RSECT, VBD_WSECT) also seem to be zero, and for sys-net-dm all the writes seem to be zero.
Is it because sys-net is a "HVM"?

Regards,
Ulrich Windl

Hi!

Watching xentop, I have a question:
I know that the network operations aren’t accounted in xentop when
running Qubes OS, but I’m wondering:
For domain-0 all of the disk I/O (VBD_RD, VBD_WR, VBD_RSECT, VBD_WSECT)
also seem to be zero,

This is because dom0 does not use paravirtualized disk drivers. Specifically, no Xen block backend device in dom0 is connected to a block frontend device in dom0, since the latter does not exist. Instead, dom0 accesses disks directly like a bare-metal OS.

If you want disk I/O statistics for dom0, you want to use something like iotop.

and for sys-net-dm all the writes seem to be zero.

DM stands for “device model,” a main role of which is to emulate the physical (i.e. non-virtualized) hardware for HVM guests that do not have the paravirtualized device drivers installed. If sys-net has all the necessary paravirtualized drivers (which almost always is the case), sys-net does not need the DM to access the disk. This is why sys-net-dm does not access the disk after boot.

Is it because sys-net is a “HVM”?

No. You’ll observe non-zero disk I/O numbers in the DM when you boot e.g. a Windows HVM without Xen paravirtualized disk drivers.

Thanks for explaining!

Ulrich