Re: + stupid-hack-to-make-mainline-build.patch added to -mm tree

Rusty Russell
2007-03-08T10:27:46Z

On Thu, 2007-03-08 at 09:01 +0100, Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>
> > > Your implementation is almost the perfect prototype, if you move the
> > > 128 bit hackery into the hypervisor and hide it away from the kernel
> > > :)
> >
> > The point is to use the tsc to avoid making any hypercalls, so dealing
> > with the tsc->ns conversion has to happen on the guest side somehow.
>
> you are obsessed with avoiding a hypercall, but why? Granted it's slow
> especially on things like SVN/VMX, but it's not fundamentally slow. We
> definitely do not want to design our whole APIs and abstractions around
> the temporary notion that 'hypercalls are slow'. I'd expect hypercalls
> to be put into silicon just as much as SYSENTER was put into silicon.

Indeed, I expect them to fall somewhere between system calls and context
switches. Perhaps not slow, but definitely worth minimising.

> Anyway, in terms of guest time code, a /big/ amount of design junk can
> be avoided by not trying to do sillynesses like 'virtual time'. The TSC
> is awfully unreliable.

You mean stolen time?

I find this whole discussion really irritating, to be honest. I just
want Thomas to implement the timer code for lguest, because that code
scares me...

I look forward to your patch 8)
Rusty.