[Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD

[Marcelo Tosatti]

On Tue, Feb 15, 2011 at 09:33:00PM +0100, Jan Kiszka wrote:
> On 2011-02-15 21:04, Marcelo Tosatti wrote:
> > On Tue, Feb 15, 2011 at 07:58:53PM +0100, Jan Kiszka wrote:
> >> On 2011-02-15 18:54, Marcelo Tosatti wrote:
> >>>
> >>> Note: to be applied to uq/master.
> >>>
> >>> In icount mode, halt emulation should take into account the nearest event 
> >>> when sleeping.
> >>>
> >>> Signed-off-by: Marcelo Tosatti <address@hidden>
> >>> Reported-and-tested-by: "Edgar E. Iglesias" <address@hidden>
> >>>
> >>> diff --git a/cpus.c b/cpus.c
> >>> index 468544c..21c3eba 100644
> >>> --- a/cpus.c
> >>> +++ b/cpus.c
> >>> @@ -770,7 +770,7 @@ static void qemu_tcg_wait_io_event(void)
> >>>      CPUState *env;
> >>>  
> >>>      while (all_cpu_threads_idle()) {
> >>> -        qemu_cond_timedwait(tcg_halt_cond, &qemu_global_mutex, 1000);
> >>> +        qemu_cond_timedwait(tcg_halt_cond, &qemu_global_mutex, 
> >>> qemu_calculate_timeout());
> >>
> >> checkpatch.pl would complain here.
> >>
> >> More important: Paolo was proposing patches to eliminate all those fishy
> >> cond_wait timeouts. That's probably the better way to go. The timeouts
> >> only paper over missing signaling.

With icount VM_TIMER timeouts are converted to realtime. This is what i
understand qemu_calculate_timeout does.

Otherwise, yes, timeouts are papering over missing signaling.

> >>
> >>>      }
> >>>  
> >>>      qemu_mutex_unlock(&qemu_global_mutex);
> >>> diff --git a/vl.c b/vl.c
> >>> index b436952..8ba7e9d 100644
> >>> --- a/vl.c
> >>> +++ b/vl.c
> >>> @@ -1335,7 +1335,7 @@ void main_loop_wait(int nonblocking)
> >>>      if (nonblocking)
> >>>          timeout = 0;
> >>>      else {
> >>> -        timeout = qemu_calculate_timeout();
> >>> +        timeout = 1000;
> >>>          qemu_bh_update_timeout(&timeout);
> >>>      }
> >>>  
> >>
> >> Isn't this path also relevant for !IOTHREAD? What's the impact of this
> >> change for that configuration?
> > 
> > Timeout changes from 5s to 1s.
> > 
> 
> ... if (!vm_running).
> 
> This patch does have side effects on !IOTHREAD. I doubt the above hunk
> can be correct.
> 
> What kind of timeout is qemu_calculate_timeout returning?

You're right.