[Qemu-devel] Re: qemu-kvm vs. qemu: Terminate cpu loop on reset?

[Gleb Natapov <gleb@redhat.com>]

On Fri, Jan 07, 2011 at 05:59:34PM +0100, Jan Kiszka wrote:
> Am 07.01.2011 17:53, Gleb Natapov wrote:
> > On Fri, Jan 07, 2011 at 04:57:31PM +0100, Jan Kiszka wrote:
> >> Hi,
> >>
> >> does anyone immediately know if this hunk from vl.c
> >>
> >> @@ -1278,6 +1197,10 @@ void qemu_system_reset_request(void)
> >>      } else {
> >>          reset_requested = 1;
> >>      }
> >> +    if (cpu_single_env) {
> >> +        cpu_single_env->stopped = 1;
> >> +        cpu_exit(cpu_single_env);
> >> +    }
> >>      qemu_notify_event();
> >>  }
> >>
> >> is (semantically) relevant for upstream as well? IIUC, it ensures that
> >> the kvm cpu loop is not continued if an IO access called into
> >> qemu_system_reset_request.
> >>
> > I don't know TCG enough to tell. If TCG can continue vcpu execution
> > after io without checking reset_requested then it is relevant for
> > upstream too.
> 
> I was first of all thinking about kvm upstream, but their handling
> differ much less upstream than in current qemu-kvm. Anyway, need to dig
> into the details.
> 
> > 
> >> If yes, then it would be a good time to push a patch: these bits will
> >> fall to dust on next merge from upstream (vl.c no longer has access to
> >> the cpu state).
> >>
> > On a next merge cpu state will have to be exposed to vl.c then. This
> > code cannot be dropped in qemu-kvm.
> 
> I think a cleaner approach, even if it's only temporarily required, is
> to move that code to cpus.c. That's likely also the way when we need it
> upstream. 
It doesn't matter where the code resides as long as it is called on
reset.

>            If upstream does not need it, we have to understand why and
> maybe adopt its pattern (the ultimate goal is unification anyway).
> 
I don't consider kvm upstream as working product. The goal should be
moving to qemu-kvm code in upstream preserving all the knowledge we
acquired while making it production grade code.

--
			Gleb.