Re: [Qemu-devel] [PATCH] qtest: add rtc periodic timer test

[Xiao Guangrong <guangrong.xiao@gmail.com>]

On 05/26/2017 12:03 AM, Paolo Bonzini wrote:
> 
> 
> On 25/05/2017 05:19, guangrong.xiao@gmail.com wrote:
>>
>> Note: as qemu needs a precise timer to drive its rtc timer callbacks,
>> that means clock=vm is not suitable for us as it's driven by icount
>> for qtest, so that we use clock=host instead, it is why we put the
>> periodic timer test separately without mixing with rtc-test
> 
> I'm not sure I understand.  Why would clock_step(1000) not be a good
> replacement for nsleep(1000)?

We can not. As we use the real time to compare with the time that is
passed in the VM, however, clock_step() is not a real time based clock
source which immediately injects a time step to the VM regardless how
much real time elapsed.

I also tried nsleep(1000) before clock_step(1000), i,e:
    nsleep(1000);
    clock_step(1000);
that can not work too, it looks like the time spend on icount update in
the VM can not be guaranteed。