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Re: [Qemu-devel] [RFC 0/5]: QMP: add balloon-get-memory-stats command
From: |
Luiz Capitulino |
Subject: |
Re: [Qemu-devel] [RFC 0/5]: QMP: add balloon-get-memory-stats command |
Date: |
Thu, 19 Jan 2012 14:58:12 -0200 |
On Thu, 19 Jan 2012 10:43:35 -0600
Michael Roth <address@hidden> wrote:
> On 01/19/2012 09:56 AM, Luiz Capitulino wrote:
> > Long ago, commit 625a5be added the guest provided memory statistics to
> > the query-balloon command. Unfortunately, it also introduced a severe
> > bug: query-balloon would hang if the guest didn't respond. This, in turn,
> > would also cause a hang in libvirt.
> >
> > Because of that, we decided to disable the guest memory stats feature
> > (commit 11724ff).
> >
> > As we decided to let commands implement ad-hoc async mechanisms until we
> > get a proper way to do it, I decided to try to re-enable that feature.
> >
> > My idea is to have a command and an event. The command gets the process
> > started by sending a request to guest and returns. Later, when the guest
> > makes the memory stats info available, it's sent to the client by means
> > of an QMP event (please, take a look at patch 05/05 for full details).
> >
> > I'm not sure if that approach is good for libvirt though, so it would be
> > very helpful to get their input (Eric, I'm CC'ing you here, but feel free
> > to route this to someone else).
> >
> > Another interesting point is that, there's another way of doing this and
> > it's using qemu-ga instead. That's, qemu-ga could read that information
> > from proc and return it. This is easier& simpler, as it doesn't involve
> > guest communication. We also could return a lot more information if needed.
> > The only disadvantage I can see is the dependency on qemu-ga...
>
> A nice plus with this is we retroactively get support for a wide range
> of existing guest types that we wouldn't realistically expect to have a
> qemu-ga package, and I think there's even balloon stats for Windows
> guests as well. Event-based updates also lend themselves nicely to
> things like qemu-centric UI integration.
>
> Memory stats is one of the proposed use-cases of qemu-ga, but I don't
> see these as necessarily being in conflict. We can extend the statistics
> collection quite a bit more with an agent approach, but it's nice to
> have some assurance that if you can balloon a guest, you can at the very
> least get at the bare minimum information you need to make reasonable
> decisions about ballooning.
That makes sense, we could have both.
>
> >
> > QMP/qmp-events.txt | 28 ++++++++++++++++++++++++++++
> > balloon.c | 47 +++++++++++++++++++++++++++++++++++++----------
> > balloon.h | 7 ++++---
> > hmp.c | 25 +------------------------
> > hw/virtio-balloon.c | 39 +++++++++++++++++++++++++++------------
> > monitor.c | 3 +++
> > monitor.h | 1 +
> > qapi-schema.json | 42 ++++++++++++++++++++++--------------------
> > qmp-commands.hx | 6 ++++++
> > 9 files changed, 129 insertions(+), 69 deletions(-)
> >
>
- [Qemu-devel] [RFC 0/5]: QMP: add balloon-get-memory-stats command, Luiz Capitulino, 2012/01/19
- [Qemu-devel] [PATCH 3/5] balloon: Drop old stats interface, Luiz Capitulino, 2012/01/19
- [Qemu-devel] [PATCH 5/5] qmp: add balloon-get-memory-stats & event, Luiz Capitulino, 2012/01/19
- [Qemu-devel] [PATCH 4/5] balloon: Rename QEMUBalloonStatus to QEMUBalloonInfo, Luiz Capitulino, 2012/01/19
- [Qemu-devel] [PATCH 2/5] balloon: Drop unused include, Luiz Capitulino, 2012/01/19
- [Qemu-devel] [PATCH 1/5] balloon: qmp_balloon(): Use error_set(), Luiz Capitulino, 2012/01/19
- Re: [Qemu-devel] [RFC 0/5]: QMP: add balloon-get-memory-stats command, Michael Roth, 2012/01/19
- Re: [Qemu-devel] [RFC 0/5]: QMP: add balloon-get-memory-stats command,
Luiz Capitulino <=
- Re: [Qemu-devel] [RFC 0/5]: QMP: add balloon-get-memory-stats command, Eric Blake, 2012/01/19
- Re: [Qemu-devel] [RFC 0/5]: QMP: add balloon-get-memory-stats command, Adam Litke, 2012/01/19