Re: Paravirt KVM capabilities

Rusty Russell
2007-01-11T03:21:36Z

On Thu, 2007-01-11 at 03:51 +0100, Ingo Molnar wrote:
> * Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org> wrote:
>
> > > > Err no, this isn't true. See Documentation/lhype.txt or various blog
> > > > entries on the subject 8) Both Xen and lhype get native syscall speeds
> > > > (within measurement error).
> > >
> > > i was talking about 64-bit. (we dont really design for 32-bit anymore.)
> [...]
> >
> > > I know that lhype uses Xen's ring 1 trick, but that's a 32-bit-only
> > > thing. Also, can SYSENTER trap from guest userspace ring 3 into guest
> > > kernelspace ring 1 on lhype?
> >
> > As I understand it, sysenter has to go to ring 0, and the reflection
> > cost is way greater than the saving.
>
> so how can both "Xen and lhype get native syscall speeds (within
> measurement error)", if it cannot use SYSENTER (it has to use int
> $0x80), while a HVM kernel can?

Sorry, my mistake. I was measuring with a statically linked binary,
which didn't use SYSENTER even when available 8(

I've fixed virtbench now, and reflects this correctly.

"syscalls almost as fast as poorly-implemented native syscalls"?
Rusty.