Re: [Xen-devel] [Patch 2 of 2]: PV-domain SMP performance Linux-part

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxxxxxxx>]

Venefax wrote:
> Just for my education and the rest of the list, what are you talking about?
> What is a PV domain compared to a Windows guest? I use the GPLPV drivers
> from James.

PV-domains are adapted to XEN in many aspects (memory management, I/O, trap
handling, ...). Instead of using the privileged x86-instructions they normally
call the hypervisor via hypercalls to perform privileged operations.

HVM-domains like Windows require virtualization support by the processor (VT-i
for INTEL, Pacifica for AMD). To boost I/O-performance, it is possible to use
PV-drivers which use a virtual PCI-device to do I/O, but most of the
privileged actions are performed as on native systems, trapping into the
hypervisor if necessary.

You could read some of the links in
http://wiki.xensource.com/xenwiki/XenArchitecture especially
http://wiki.xensource.com/xenwiki/XenArchitecture?action=AttachFile&do=get&target=Xen+Architecture_Q1+2008.pdf
http://www.linuxjournal.com/article/8540 and
http://www.linuxjournal.com/article/8909 might be useful.

My patches require special actions in the domain to avoid descheduling in
critical paths. In Windows this is normally an area covered by HAL, so you
would have to port HAL to be XEN-aware, which I think would be a task for
Microsoft to do...

Juergen

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