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

[Marcelo T. <mto...@re...>]

On Tue, Apr 29, 2008 at 05:42:51PM -0500, Anthony Liguori wrote:
> Marcelo Tosatti wrote:
> >Hi Anthony,
> >
> >How is -no-kvm-irqchip working with the patch?
> >  
> 
> Seems to work fine.  What is your expectation?

Just wondering if vcpu's are being properly awake.

> >Make sure the IO thread has SIG_IPI blocked (those are for APIC vcpu
> >initialization only).
> >  
> 
> Just so I'm clear, there's really no harm in not blocking SIG_IPI 
> because it would just be ignored by the IO thread (since the SIG_IPI 
> handler is a nop).  But yeah, we should explicitly block it.

Problem is if the IO thread _receives_ SIGIPI instead of some vcpu
thread. 

So there is potential harm in not blocking it.

> >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 :-)

> >>-        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.