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[Xen-users] Does I/O from Dom0 skip the PV backend drivers ?

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Does I/O from Dom0 skip the PV backend drivers ?
From: Joe Armstrong <Joe.Armstrong@xxxxxxxxx>
Date: Wed, 29 Apr 2009 13:45:02 -0700 (PDT)
Delivery-date: Wed, 29 Apr 2009 13:45:50 -0700
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I am trying to determine the amount of overhead (if any) that a PV guest
incurs as compared to running on bare metal.  I was thinking of running some
performance tests on both a bare metal system and then in a PV guest – but I
only have one machine.  I am trying to figure out if  booting from a xen to
non-xen kernel is needed in order to get real numbers.

So the question boils down to – When Dom0 performs I/O does it go directly
to the physical device driver or does it also route through the PV backend
drivers ?

Also, my assumption is that the xen hypervisor has no role in any I/O
operations so it being present or not should have almost no impact on I/O

Thanks for any info.


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