Re: [Qemu-devel] [PATCH 6/6] qmp: add balloon-get-memory-stats & event

[Anthony Liguori <aliguori@us.ibm.com>]

On 02/08/2012 02:30 PM, Luiz Capitulino wrote:
> This commit adds a QMP API for the guest provided memory statistics
> (long disabled by commit 07b0403dfc2b2ac179ae5b48105096cc2d03375a).
>
> The approach taken by the original commit
> (625a5befc2e3200b396594f002218d235e375da5) was to extend the
> query-balloon command. It introduced a severe bug though: query-balloon
> would hang if the guest didn't respond.
>
> The approach taken by this commit is asynchronous and thus avoids
> any QMP hangs.
>
> First, a client has to issue the balloon-get-memory-stats command.
> That command gets the process started by only sending a request to
> the guest, it doesn't block. When the memory stats are made available
> by the guest, they are returned to the client as an QMP event.
>
> Signed-off-by: Luiz Capitulino<lcapitulino@redhat.com>

Do we need this to be stable in 1.1?

We can do this pretty nicely through QOM.  We can have a polling property in the 
virtio-balloon driver, that when set, will enable the virtio-balloon device to 
poll the guest for statistics.

We can also have properties for each of the memory statistics and a timestamp 
for when the last update was.

I think this is a friendlier approach for clients, and a cleaner approach from a 
QEMU perspective.

There's nothing generic about this functionality.  It's extremely specific to 
virtio-balloon.  We just lacked ways to expose device specific function pre-QOM.

Regards,

Anthony Liguori