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

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Apr 29, 2008 at 06:44:29PM -0500, Anthony Liguori wrote:
> Marcelo Tosatti wrote:
> >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.
> >  
> 
> If  you're getting that many signals, then select() is never going to 
> run anyway.

True.

Either way, this starvation due to signals can't happen with the current
scheme because signals are blocked. It seems a significant drawback.

Moving the signal handling + pipe write to a separate thread should get
rid of it.

> No, they're independent of the patch.  The symptom is that the guest 
> tends to hang during boot for prolonged periods of time.  It tends to be 
> random whether it will hang at all, how long it will hang, and at what 
> point it will hang.  It tends to hang more often in particular places.  
> In my ubuntu server guest, for instance, it tends to hang right after 
> partition probing, right after "Loading hardware drivers", and right 
> before spawning a getty on /dev/tty0.
> 
> Normally, it will only hang for a few seconds.  However, with -smp N 
> where N > number of cpus in the host, it tends to happen more 
> frequently.  Using clock=jiffies in the guest makes the problem go away.

I'll try to reproduce that, thanks.

> -no-kvm-pit doesn't make a difference (the guest is normally using the 
> pm-timer).
> 
> Regards,
> 
> Anthony Liguori

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