Re: [Qemu-devel] [Bug 1021649] Re: qemu 1.1.0 waits for a keypress at boot

[Avi Kivity]

On 07/25/2012 02:12 PM, Stefano Stabellini wrote:
> On Wed, 25 Jul 2012, Michael Tokarev wrote:
>> Stefano, Paul, can you take a look please?
>> 
>> https://bugs.launchpad.net/bugs/1021649
> 
> That is a very good bug triage that you did!
> 
> However "main_loop_wait: block indefinitely" only increases the maximum
> select timeout of QEMU's main_loop.
> That mean that if one or more emulators have bugs and don't get
> notifications correctly they might hang.
> The reason why it only reproduces with nographic is that both sdl and vnc
> introduce a gui_timer that wakes QEMU up every 30ms.
> 
> So the question is: why is kernel_irqchip=on required to repro the bug?
> It strikes me as a bug in kernel_irqchip that prevents QEMU from being
> waken up when it should.

kernel_irqchip=on means that many guest timers and interrupt sources are
removed from qemu and implemented in the kernel, so qemu sees a lot less
wakeups and hangs.  With kernel_irqchip=off the APIC or PIT wakes up
qemu, taking the place of the keypress.

-- 
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