Re: [Qemu-devel] [PATCH 5/6] [RFC] Emulation of Leon3.

[Fabien Chouteau]

On 12/17/2010 08:14 PM, Blue Swirl wrote:
> On Wed, Dec 15, 2010 at 5:47 PM, Fabien Chouteau<address@hidden>  wrote:
> > On 12/13/2010 07:18 PM, Blue Swirl wrote:
> > > On Mon, Dec 13, 2010 at 3:51 PM, Fabien Chouteau<address@hidden>
> > >   wrote:
> > > > On 12/11/2010 10:56 AM, Blue Swirl wrote:
> > > > > On Tue, Dec 7, 2010 at 11:40 AM, Fabien Chouteau<address@hidden>
> > > > >   wrote:
> > > > > > On 12/06/2010 06:53 PM, Blue Swirl wrote:
> > > > > > > On Mon, Dec 6, 2010 at 9:26 AM, Fabien Chouteau<address@hidden>
> > > > > > >   wrote:
> > > > > > >
> > > > > > > > +#if !defined(CONFIG_USER_ONLY)
> > > > > > > > +    /* Leon3 shutdown */
> > > > > > > > +    if (intno == 0x80&&        env->version == 0xf3000000) {
> > > > > > > > +        leon3_shutdown();
> > > > > > > > +    }
> > > > > > >
> > > > > > > This looks like a hack. Should a trap instruction initiate a shutdown?
> > > > > >
> > > > > > Yes, on Leon3 "ta 0x0" initiates a shutdown.
> > > > >
> > > > > Then this should be handled during translation. A Leon3 specific CPU
> > > > > feature should be added and used much like CHECK_IU_FEATURE (in
> > > > > translate.c). Then execution speed would not be affected for non-Leon3
> > > > > CPUs.
> > > >
> > > > OK, but I don't see how to request a shutdown during translation.
> > >
> > > Just create a helper which calls shutdown, translator should insert a
> > > call to that.
> >
> > I think I understand what you mean, but I don't see why this would be faster
> > than my solution.
>
> Shutdown is not performance critical, but interrupt handling is.

I understand that, but why is it faster to do it during translation?

I don't see how one "if" statement in "do_interrupt" will even slightly 
impact
the performances, and why it will be slower than the same "if' statement 
in the translation.

BTW, I didn't use the "unlikely" function, but this will even more 
reduce the impact...

--
Fabien Chouteau