timer: set vm_clock disabled default

(commit 80dcfb8532ae76343109a48f12ba8ca1c505c179)
Upon migration, the code use a timer based on vm_clock for 1ns
in the future from post_load to do the event send in case host_connected
differs between migration source and target.

However, it's not guaranteed that the apic is ready to inject irqs into
the guest, and the irq line remained high, resulting in any future interrupts
going unnoticed by the guest as well.

That's because 1) the migration coroutine is not blocked when it get EAGAIN
while reading QEMUFile. 2) The vm_clock is enabled default currently, it doesn't
rely on the calling of vm_start(), that means vm_clock timers can run before
VCPUs are running.

So, let's set the vm_clock disabled default, keep the initial intention of
design for vm_clock timers.

Meanwhile, change the test-aio usecase, using QEMU_CLOCK_REALTIME instead of
QEMU_CLOCK_VIRTUAL as the block code does.

CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
CC: qemu-stable@nongnu.org
Signed-off-by: Gonglei <arei.gonglei@huawei.com>
---
 qemu-timer.c     | 2 +-
 tests/test-aio.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

On 09/08/2016 09:49, Gonglei wrote:
> (commit 80dcfb8532ae76343109a48f12ba8ca1c505c179)
> Upon migration, the code use a timer based on vm_clock for 1ns
> in the future from post_load to do the event send in case host_connected
> differs between migration source and target.
> 
> However, it's not guaranteed that the apic is ready to inject irqs into
> the guest, and the irq line remained high, resulting in any future interrupts
> going unnoticed by the guest as well.
> 
> That's because 1) the migration coroutine is not blocked when it get EAGAIN
> while reading QEMUFile. 2) The vm_clock is enabled default currently, it doesn't
> rely on the calling of vm_start(), that means vm_clock timers can run before
> VCPUs are running.
> 
> So, let's set the vm_clock disabled default, keep the initial intention of
> design for vm_clock timers.
> 
> Meanwhile, change the test-aio usecase, using QEMU_CLOCK_REALTIME instead of
> QEMU_CLOCK_VIRTUAL as the block code does.
> 
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
> CC: qemu-stable@nongnu.org
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
>  qemu-timer.c     | 2 +-
>  tests/test-aio.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/qemu-timer.c b/qemu-timer.c
> index eb22e92..9299cdc 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -129,7 +129,7 @@ static void qemu_clock_init(QEMUClockType type)
>      assert(main_loop_tlg.tl[type] == NULL);
>  
>      clock->type = type;
> -    clock->enabled = true;
> +    clock->enabled = (type == QEMU_CLOCK_VIRTUAL ? false : true);
>      clock->last = INT64_MIN;
>      QLIST_INIT(&clock->timerlists);
>      notifier_list_init(&clock->reset_notifiers);
> diff --git a/tests/test-aio.c b/tests/test-aio.c
> index 982339c..03aa846 100644
> --- a/tests/test-aio.c
> +++ b/tests/test-aio.c
> @@ -452,7 +452,7 @@ static void test_timer_schedule(void)
>  {
>      TimerTestData data = { .n = 0, .ctx = ctx, .ns = SCALE_MS * 750LL,
>                             .max = 2,
> -                           .clock_type = QEMU_CLOCK_VIRTUAL };
> +                           .clock_type = QEMU_CLOCK_REALTIME };
>      EventNotifier e;
>  
>      /* aio_poll will not block to wait for timers to complete unless it has
> @@ -782,7 +782,7 @@ static void test_source_timer_schedule(void)
>  {
>      TimerTestData data = { .n = 0, .ctx = ctx, .ns = SCALE_MS * 750LL,
>                             .max = 2,
> -                           .clock_type = QEMU_CLOCK_VIRTUAL };
> +                           .clock_type = QEMU_CLOCK_REALTIME };
>      EventNotifier e;
>      int64_t expiry;
>  
> 

Good fix!  I'll queue it for 2.7.

Paolo