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

[Wayne Sun]

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?

Wayne Sun
2012-11-27
>
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