Re: [Qemu-devel] [Qestion] What status of memory stats feature

[Luiz Capitulino <lcapitulino@redhat.com>]

On Wed, 15 Dec 2010 16:20:05 +0900
"Ken'ichi Ohmichi" <oomichi@mxs.nes.nec.co.jp> wrote:

> 
> Hi,
> 
> I tried to get the memory stats by using virDomainMemoryStats() of libvirt,
> but it could not do it because of the following patch:
> 
> [PATCH 03/23] disable guest-provided stats on "info balloon" command
>   2010/10/01 from Luiz Capitulino
>   http://www.mail-archive.com/qemu-devel@nongnu.org/msg43024.html 
> 
> According to the related thread, the above patch avoids hanging user
> monitor, and people hope the memory stats feature will be able in the
> future. So I'd like to know the status of this feature.
> 
> Is there the patch for enabling the feature ?
> If the patch exists, I'd like to try it.

It doesn't, afaik.

> What is the essential problem ?

There are two essential problems here.

The first one is that QMP lacks true asynchronous command support (it does
have some code for it, but it's incomplete).

The second problem is that we must not make an existing synchronous command
asynchronous, because this breaks the ABI.

> Does some infinite loop happen ?

No, the guest doesn't respond.

> Unfortunately, I cannot understand the cause of hanging user monitor.

The balloon command needs guest cooperation (ie. it talks to the guest),
if the guest doesn't respond the command will never return.

We don't have a precise ETA for async support, but if it depends only on
the new error framework work, then we could have it for 0.15. If it depends
on the full monitor redesign work, then I guess we'll two releases.