[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC][PATCH 03/10] xen/hybrid: Xen Hybrid Extension initialization
On 09/16/09 01:42, Sheng Yang wrote: > As we know that PV guest have performance issue with x86_64 that guest kernel > and userspace resistent in the same ring, then the necessary TLB flushes when > switch between guest userspace and guest kernel cause overhead, and much more > syscall overhead is also introduced. The Hybrid Extension estimated these > overhead by putting guest kernel back in (non-root) ring0 then achieve the > better performance than PV guest. > > The Hybrid Extension is started from real mode like HVM guest, but also with a > component based PV feature selection(e.g. PV halt, PV timer, event channel, > then PV drivers). So guest with Hybrid extension feature can takes the > advantages of both H/W virtualization and Para-Virtualization. > > This patch introduced the Hybrid Extension guest initialization. > > Guest would detect Hybrid capability using CPUID 0x40000002.edx, then call > HVMOP_enable_hybrid hypercall to enable hybrid support in hypervisor. > I think having an option to put PV guests into an HVM container is a good one, but as I mentioned in the other mail, I don't think this is the right approach. It would be much better to make it so that an unmodified guest works in such a mode; even with no specific optimisations the guest would get benefit from faster kernel<->usermode switches. Then we can add specific optimisations to take advantage of, say, running in ring 0 (=fast syscalls) and having access to HAP hardware (=direct pagetable updates, no pinning). J _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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