[Qemu-devel] Re: [PATCH v3] introduce on_vcpu

[Glauber Costa]

On Thu, Aug 27, 2009 at 07:15:28PM +0200, Jan Kiszka wrote:
> Glauber Costa wrote:
> > on_vcpu is a qemu-kvm function that will make sure that a specific
> > piece of code will run on a requested cpu. We don't need that because
> > we're restricted to -smp 1 right now, but those days are likely to end soon.
> > 
> > So for the benefit of having qemu-kvm share more code with us, I'm
> > introducing our own version of on_vcpu(). Right now, we either run
> > a function on the current cpu, or abort the execution, because it would
> > mean something is seriously wrong.
> > 
> > As an example code, I "ported" kvm_update_guest_debug to use it,
> > with some slight differences from qemu-kvm.
> > 
> > This is probably 0.12 material
> > 
> > Signed-off-by: Glauber Costa <address@hidden>
> > CC: Jan Kiszka <address@hidden>
> > ---
> >  kvm-all.c |   35 +++++++++++++++++++++++++++++------
> >  1 files changed, 29 insertions(+), 6 deletions(-)
> > 
> > diff --git a/kvm-all.c b/kvm-all.c
> > index 61194b8..07a1cdb 100644
> > --- a/kvm-all.c
> > +++ b/kvm-all.c
> > @@ -155,6 +155,15 @@ static void kvm_reset_vcpu(void *opaque)
> >      }
> >  }
> >  
> > +static void on_vcpu(CPUState *env, void (*func)(void *data), void *data)
> > +{
> > +    if (env == cpu_single_env) {
> > +        func(data);
> > +        return;
> > +    }
> > +    abort();
> 
> Sorry, missed this before it went in: This abort fires already now when
> kvm_update_guest_debug is invoked by the gdbstub (where cpu_single_env
> is 0). This completely breaks guest debugging int kvm mode.
> 
> Moreover, if you enable I/O thread support, you already have a need for
> true on_vcpu, don't you? Or is locking around the I/O thread still
> broken in kvm mode? Anyway, please fix.
It is, but I just sent two patches that would leave us in a better shape.
Not sure what was made of them.

Anyway, I still have something almost ready for on_vcpu.
Actually, I want to hear input on it: I was thinking the best architecture
would be to drop it completely, and do automatically whenever we call 
vcpu_ioctl.
My only concern then would be speed. In this case, we could make this 
non-blocking,
and introduce explicit flush requests for remote cpus.

What do you think about it ?