[RFC] Performance monitoring units and KVM

[Balaji Rao <balajirrao@gmail.com>]

Hi all!

Earlier it was suggested that we go ahead with emulating Perf Mon Events in 
exposing it to the guest. The serious limitation in this approach is that we 
end up exposing only a small number of events to the guest, even though the 
host hardware is capable of much more. The only benefit this approach offers is 
that, it doesn't break live migration.

The other option is to pass through the real PMU to the guest. I believe this 
approach is far better in the sense that,

1. All the available events in the host hardware can be passed on to the guest, 
which can be used by oprofile to profile the guest and trackdown slowdowns 
introduced due to virtualization.

2. Its much cleaner and easier to pass through the PMU.

Yes, this approach breaks live migration. Migration should not be possible 
*only* when the PMU is being used by oprofile. We can mark the guest as 
unmigratable in such situations. Once the PMU is not being used, migration can 
be performed normally.

Note, this requires a small change to oprofile source. Upon migration, oprofile 
should be made to re-identify the CPU and use the perf mon events appropriate 
to that CPU. I think this could be done by having a migrate_notifier, or 
something like that..

Please provide comments on this.

-- 
regards,
balaji rao
NITK

-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/