Re: The reason of using Qcow images to boot smp Windows fail ?

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Liu, Eric E wrote:
> Hi Avi
> 	For current commit Windows SMP guests will fail to boot if using
> Qcow images based on the original backend file on a remote network file
> system.  I found out that one Ap thread is hang at the place of
> bdrv_read_em() -> qemu_aio_wait() -> sigwait(), which is waiting for the
> signal SIGUSR2. Since AIO thread sends a SIGUSR2 to QEMU to indicate the
> completion of an AIO request, and if we use Qcow img, it will wait for
> the signal. In current code we don't mask the signal SIGUSR2 in VCPU0 's
> thread, so it may eat the signal the Ap thread is waiting for. if I mask
> the signal as fellow: 
>
>   1 diff --git a/qemu/qemu-kvm.c b/qemu/qemu-kvm.c
>   2 index 9aee903..9fe4235 100644
>   3 --- a/qemu/qemu-kvm.c
>   4 +++ b/qemu/qemu-kvm.c
>   5 @@ -310,9 +310,10 @@ static void setup_kernel_sigmask(CPUState *env)
>   6
>   7      sigprocmask(SIG_BLOCK, NULL, &set);
>   8      sigdelset(&set, SIG_IPI);
>   9 -    if (env->cpu_index == 0)
>  10 +    if (env->cpu_index == 0) {
>  11         sigandset(&set, &set, &io_negsigset);
>  12 -
>  13 +       sigaddset(&set, SIGUSR2);
>  14 +    }
>  15      kvm_set_signal_mask(kvm_context, env->cpu_index, &set);
>  16  }
>
>  Windows SMP guests will boot successfully. I am not very clear that why
> we don't mask it, do you have other consideration? thx.
>
>   

The intent was that vcpu 0 will handle all I/O and timers, simply to be 
similar to regular qemu.  But as you say, this breaks aio, so we should 
remove SIGUSR2 from io_sigset and io_negsigset and enable it like SIG_IPI.

Longer term I'd like to move network I/O and alarm handling to a 
separate thread to reduce vmexits, but that's a separate issue.

-- 
error compiling committee.c: too many arguments to function


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