[libvirt] [test-API][PATCH] balloon_memory: add time break before dump xml

[Guannan Ren]

On 11/27/2012 07:01 PM, Wayne Sun wrote:
> On 11/27/2012 04:36 PM, Guannan Ren wrote:
>> On 11/27/2012 03:02 PM, Wayne Sun wrote:
>>> the xml dumped after setMemory is not accurate due to time
>>> delay, so take 10 sec sleep before dump to show the right
>>> xml info
>>
>>         Why it is necessary to sleep for a while, I don't think 
>> adding a sleep
>>       is a good way to solve problem.
>>         Please try to figure out the root cause.
>>
>>       Guannan
>>
> DB recently change the code of get domain memory balloon value as in 
> patch:
> http://www.redhat.com/archives/libvir-list/2012-May/msg00871.html
>
> If QEMU supports the BALLOON_EVENT QMP event, then we can
> avoid invoking 'query-balloon' when returning XML or the
> domain info.
>
> And in qemu patch:
> http://lists.gnu.org/archive/html/qemu-devel/2012-05/msg02833.html
>
> DB also emphasis in description:
>
> It is important to note that events are only discarded when they are
> obsoleted by a newer event. So an application is guarenteed to see the
> final balloon event, with at worst a 1 second delay.
>
> So when after do memory change, for dump domain xml to get balloon 
> value, it will be controlled in 1 second delay.
>
> When i check with QMP with query-events commands on 
> qemu-kvm-rhev-0.12.1.2-2.337.el6.x86_64:
> { "execute": "query-events"}
> {"error": {"class": "CommandNotFound", "desc": "The command 
> query-events has not been found", "data": {"name": "query-events"}}}
>
> and this also in my log, so my qemu did not support this BALLOON_EVENT 
> and using query-balloon to get current memory, and indeed 
> 'query-balloon' is spotted in my log.
>
> This back to
> # vim src/qemu/qemu_driver.c +5330
>
>         /* Don't delay if someone's using the monitor, just use
>          * existing most recent data instead */
>
> so most recent data will be returned with query-balloon, that means if 
> we query too fast, the result will not be accurate.
>
> I think add little time sleep is reasonable here for now, but after 
> qemu support BALLOON_EVENT, then the sleep will be no use.
>
> So, what do you think?

      Okay,  I got what you meant here, 10 seconds is too long, I plan 
to change it to 3 seconds as we discussed.
      Thanks for your patch.

      Guannan Ren