Re: [Qemu-devel] about the patch kvmclock Ensure proper env->tsc value for kvmclock_current_nsec calculation

[Li, Liang Z]

> >>>      Could please point out what issue the patch 317b0a6d8ba44e try
> >>> to fix?  I
> >> found in live migration the cpu_synchronize_all_states will be called
> >> twice, and it will take more than 1 ms sometimes. I try to do some
> >> optimization but lack the knowledge about the background.
> >>
> >> What the code in 317b0a6d8ba44e requires is to retrieve the TSC value
> >> from the kernel.
> >
> > I know 317b0a6d8ba44e is to retrieve the TSC value, but I don't understand
> why it is needed. During the live migration, the cpu_synchronize_all_states
> will be called later after stopping kvm-clock. The env->tsc will be updated, 
> is
> that not enough? Or is there some case like call the
> 'stop_vm(RUN_STATE_PAUSED )' or ' 'stop_vm (RUN_STATE_DEBUG) ', that
> require updating the env->tsc? By google, I find that your patch try to fix
> some issue, but I don't know what the exact issue.
> 
> I remember testing these, and I afair that was the reason:
> 
> http://lists.gnu.org/archive/html/qemu-devel/2014-06/msg00472.html
> 
> --
> mg

Hi Mg,

    Thanks for your reply, I have read the thread in your email, what's the 
mean of 'switching from old to new disk', could give a detail description? 

Liang