On Thu, May 31, 2007 at 04:58:41AM -0700, Stephane Eranian wrote: > Avi, > > On Thu, May 31, 2007 at 02:52:05PM +0300, Avi Kivity wrote: > > Stephane Eranian wrote: > > >> > > >>If the guest cpuid is set to a least common denominator, it should work. > > >> > > >> > > >There is no common denominator between a P4 and Intel Core 2 Duo for the > > >performance counters. So you cannot simply use a generic member of family > > >15 to fake the guest cpuid runnning on Intel Core 2 Duo host. > > > > > > > > > > So, the performance counter functionality will not be available if you > > have a mixed server farm with these processors. > > > That's like what is going to happen. > > > If applications use model version to detect performance counters, and > > not cpuid bits, then there is no way to prevent guests using performance > > counters. Fortunately this is limited to specialized applications. > > > They use cpuid. I expect more and more applications/OS will rely on > performance counters to boost performance at runtime.
This sounds like a huge headache waiting to happen, and something that could end up giving virtualization and KVM a bad name in the long run, due to the inevitable bugs and performance problems that will happen with end-users that don't know the details about what performance counters are supported on what cpu model. The only halfway sane solution I can think of involves having guest support for CPU hotplug, so that a host can notify a guest that the underlying CPU has changed. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kvm-devel
