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

["Marcin Gibuła" <m.gibula@beyond.pl>]

W dniu 2015-08-14 o 03:23, Li, Liang Z pisze:
>> On Thu, Aug 13, 2015 at 01:25:29AM +0000, Li, Liang Z wrote:
>>> Hi Paolo & Marcelo,
>>>
>>>      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