On 16.11.2010, at 19:22, Anthony PERARD wrote: > On Tue, 16 Nov 2010, Anthony Liguori wrote: > >> On 11/16/2010 11:24 AM, Alexander Graf wrote: >>> On 16.11.2010, at 18:20, Anthony Liguori wrote: >>> >>> >>>> On 11/16/2010 10:59 AM, Alexander Graf wrote: >>>> >>>>> >>>>>> Surely, only if it is running on a Xen Dom0. If you use -M xenpv on a KVM >>>>>> host, then -M xenpv should imply -machine accel=kvm (ie it would be using >>>>>> xenner) >>>>>> >>>>>> >>>>> Actually, it should imply -machine accel=kvm,tcg :). Accelerators really >>>>> are not a machine property. In an ideal world, -M pc would just work with >>>>> xen hvm if -accel xen is given. >>>>> >>>>> >>>> No, an accelerator is both a CPU selection and a machine characteristic. >>>> For KVM, we overload -cpu to modify both the KVM CPU and the TCG CPU both >>>> this won't work with accel=xen. We probably shouldn't do this with KVM >>>> either because there's a significant different between trying to do cpuid >>>> masking with KVM and modifying the TCG cpu emulation support. >>>> >>>> Both KVM and Xen have other impacts on the platform devices though. KVM >>>> does not support SMM so it disables that in the i440fx. KVM prefers to >>>> use it's own in-kernel local APIC (and IOAPIC). That makes it a property >>>> of the machine. >>>> >>> So you're saying the machine should define an accel mask of accels it >>> supports? >>> >>> However all this ends up internally, giving the user an easy option to >>> choose accels would still be nice. Users don't use -device or -machine. >>> They want shortcuts :). >>> >> >> User's want things to just work. >> >> That's why -M xenpv should imply -machine accel=xen. > > Actually, it works like that for qemu-xen, we just specify -M xenpv, and > we don't have any --enable-xen or other -accel xen.
Yes, and that's exactly the behavior you'd get :). -accel would default to xen,kvm,tcg and thus -M xenpv on xen defaults to real xen pv code, -M xenpv on kvm would default to xenner w/ kvm and -M xenpv without any accelerator available would just fall back to xenner with tcg. Everyone is happy :). Alex
