Re: [Qemu-devel] qemu vl.c

[Avi Kivity]

Paul Brook wrote:
> On Sunday 16 December 2007, Anders wrote:
>   
> > Paul Brook wrote:
> >     
> > > >         Redundant timer rearm optimisation by Anders Melchiorsen.
> > > >         
> > > I think this is incorrect.
> > >
> > > When a timer is modified, we need to rearm the host timer immediately. We
> > > can not wait for the old timer to fire, or for execution to fall back to
> > > the main_loop_wait.  Consider the case where the guest adds a timer
> > > interrupt and immediately enters a tight loop - Quite a common operation
> > > when calibrating a software delay loop. The timer won't be rearmed until
> > > some other event occurs. It the system is otherwise quiescent and you're
> > > not using SDL output it may never occur.
> > >       
> > Hi Paul,
> >
> > I am certainly open to it not being correct, but currently I fail to see
> > how it changes the scenario that you mention. The rearming is moved away
> > from qemu_run_timers(), not qemu_mod_timer(). Can you elaborate?
> >     
>
> It's possible that this code has always been broken. You changes make it much 
> more obviously so.
>
>   

I'm merging qemu-cvs into the kvm repository now, and with this commit 
in, kvm will hang after about a minute.  Attaching to it with gdb or 
strace will cause it to resume, so this is very likely a missing signal 
problem.

(qemu will happily run with this patch; kvm is much more sensitive to 
missed signals).


--
Any sufficiently difficult bug is indistinguishable from a feature.