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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