Avi Kivity wrote: > Anthony Liguori wrote: >> Avi Kivity wrote: >>> Anthony Liguori wrote: >>>> Howdy, >>>> >>>> Does anyone know what the state of a pv_ops backend for KVM is? I >>>> know Ingo has an implementation that implements CR3 caching but I >>>> don't see any branches in Avi's git tree. >>>> >>>> Perhaps we should try for a simple pv_ops backend for 2.6.23 seeing >>>> as how the host infrastructure is there? I'd be willing to do some >>>> leg work here... >>> >>> I think we should aim for a full direct paging implementation, where >>> the cr3 cache is just the cherry on top that makes context switches >>> proceed at native speed. Jun has a paper on it for OLS and I hope >>> patches too. >> >> That's a bit more ambitious than I was thinking. I would be very >> happy with a pv timer, interrupt controller, and some basic CPU >> optimizations. I'm still not convinced the perf benefits of direct >> paging justify the annoyances that come with it (guests being aware >> of pfns). > > I thought that with paravirt_ops, all the awareness is limited to the > paravirt implementation, and nothing in the core kernel is actually > aware of host pfns.
The pv_ops implementation still has to deal with guest pfn => host pfn translation. This means that a guest has to be put into a special mode for save/restore/migrate to work to ensure that no host pfn's are on the stack or in registers. Changing save/restore/migration to from guest-transparent to guest-interactive is a big loss to me. > pv timer and interrupt controller make a lot of sense, especially if > steal timer functionality is included. Yup :-) >> This is especially true with NPT/EPT right around the corner. > > It depends on the workload. It was advanced (by Ingo) that NPT/EPT > increase the tlb miss latency, which is important for steady-state > workloads, whereas shadow and direct paging do not. It will be > interesting to measure this. There will most certainly be trade-offs, but I certainly don't expect direct paging to beat out NPT/EPT in certain areas. Regards, Anthony Liguori ------------------------------------------------------------------------- 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 kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
