Re: [Qemu-devel] [RFC 09/10] cpu: remove exit_request global.

[Frederic Konrad]

On 29/01/2015 16:52, Peter Maydell wrote:
> On 16 January 2015 at 17:19,  <address@hidden> wrote:
> > From: KONRAD Frederic <address@hidden>
> >
> > This removes exit_request global and adds a variable in CPUState for this.
> > Only the flag for the first cpu is used for the moment as we are still with one
> > TCG thread.
> > --- a/cpus.c
> > +++ b/cpus.c
> > @@ -646,10 +646,14 @@ static void cpu_handle_guest_debug(CPUState *cpu)
> >
> >   static void cpu_signal(int sig)
> >   {
> > +    CPUState *cpu;
> >       if (current_cpu) {
> >           cpu_exit(current_cpu);
> >       }
> > -    exit_request = 1;
> > +
> > +    CPU_FOREACH(cpu) {
> > +        cpu->exit_loop_request = 1;
> > +    }
> >   }
> You can't do this -- this code is a signal handler so it could
> get run at any time including while the list of CPUs is being
> updated. (This is why we have the exit_request flag in the
> first place rather than just setting the exit_request flag in
> each CPU...)
>
> Possibly you want exit_request to be a per-thread variable,
> but I haven't thought much about it.
>
> > --- a/include/qom/cpu.h
> > +++ b/include/qom/cpu.h
> > @@ -249,6 +249,7 @@ struct CPUState {
> >       bool created;
> >       bool stop;
> >       bool stopped;
> > +    volatile sig_atomic_t exit_loop_request;
> >       volatile sig_atomic_t exit_request;
> >       uint32_t interrupt_request;
> >       int singlestep_enabled;
> This would duplicate the exit_request and
> exit_loop_request flags in the CPU, which is kind of odd.
>
> -- PMM
Actually, what we want to do is remove exit_requested global because 
when it exits
the loop in tcg_exec_all it does exit_requested = 0, and other vcpu 
doesn't exit.

This is not clear to me why we have both exit_requested global and 
exit_request in
CPUState.

Maybe we can just make exit_request thread local this might work.

Also, we need to be able to exit VCPU we want from a TCG thread.
eg: We want to flush all the tlb we need to exit all cpus but one..

Thanks,
Fred