Re: [PATCH][RFC] Use pipe() to simulate signalfd()

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Apr 29, 2008 at 06:15:58PM -0500, Anthony Liguori wrote:
> Marcelo Tosatti wrote:
> >Problem is if the IO thread _receives_ SIGIPI instead of some vcpu
> >thread. 
> >
> >So there is potential harm in not blocking it.
> >  
> 
> Hrm, aren't SIG_IPIs delivered to a particular thread-id though?  When 
> would the IO thread receive a SIG_IPI?

Right, they are only delivered to specific threads. Still not harmful 
to make it explicit.

> >>>What is the reason for this loop instead of a straight read? 
> >>>
> >>>Its alright to be interrupted by a signal.
> >>> 
> >>>      
> >>Just general habit with QEMU.
> >>    
> >
> >Please don't :-)
> >  
> 
> I don't see the harm.  In fact, I think it's more correct.  Otherwise, 
> we have to wait for another invocation of the fd callback.

Why? If you leave data in the pipe the next select() won't block.

Isnt there the possibility that this loop can be stuck for significant
amounts of time? If you're receiving lots of notifications through
signals.

> >>>>-        kvm_eat_signal(&io_signal_table, NULL, 1000);
> >>>>        pthread_mutex_lock(&qemu_mutex);
> >>>>-        cpu_single_env = NULL;
> >>>>-        main_loop_wait(0);
> >>>>+	main_loop_wait(10);
> >>>>   
> >>>>        
> >>>Increase that 1000 or something. Will make it easier to spot bugs.
> >>> 
> >>>      
> >>I have actually and it does introduce some bugs.  I'm not entirely clear 
> >>what is causing them though.
> >>    
> >
> >Should indicate that some event previously delivered through signals and
> >received by sigtimedwait is not waking up the IO thread.
> >  
> 
> I'll take a look and see.  I'm having time keeping issues in the guest 
> so it's hard to tell what problems are caused by the IO thread verses time.

Time issues only with the patch? If not, please share details.


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