Re: [Qemu-devel] Multiple instances of Qemu on Windows multicore

[malc]

On Wed, 2 Nov 2011, Fabien Chouteau wrote:

> On 02/11/2011 17:25, Paolo Bonzini wrote:
> > On 11/02/2011 04:38 PM, Fabien Chouteau wrote:
> >> Hello fellow Qemu aficionados,
> >>
> >> On Windows, Qemu sets the affinity mask in order to run all thread on
> >> CPU0, with this comment in the code (os-win32.c:182):
> >>
> >>      /* Note: cpu_interrupt() is currently not SMP safe, so we force
> >>         QEMU to run on a single CPU */
> >>
> >> This was added by Fabrice Bellard in 2006 (git show a8e5ac33d).
> >>
> >> I can't find/understand any reason for this CPU affinity restriction.
> > 
> > Have you tried looking for a justification in the mailing lists?
> 
> Yes, and I found few mails from Fabrice Bellard and Konrad Schwarz in
> the archives:
> 
> http://thread.gmane.org/gmane.comp.emulators.qemu/13804
> 
> and
> 
> http://thread.gmane.org/gmane.comp.emulators.qemu/13831/focus=13805
> 
> But it didn't provide more information about the problem.
> 
> >
> > Also, I suppose you have tested without the affinity mask and it works?
> >
> 
> Yes I did, it works pretty well. I had 1 unexpected failure among ~6000
> tests. But I would like to have a substantial explanation.
> 
> >
> > Offhand I cannot think of why that would be needed.
> >
> 
> OK, thanks for your help.

(mm)Timers have a possibility of running on a thread of their own which
might be schedulled on the CPU different from the thread that runs 
emulated code, unchaining TBs and can (and will) fail in this case.

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