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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: |
Fri, 20 Jan 2012 10:06:24 -0200 |
On Thu, 19 Jan 2012 15:50:06 -0600
Adam Litke <address@hidden> wrote:
> On Thu, Jan 19, 2012 at 01:56:26PM -0200, 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...
> >
> > 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(-)
> >
>
> The patch series looks good. Thanks for making the improvements. Once it is
> upstream I can help out with the libvirt pieces. I tested it with a Fedora-15
> VM and it worked out of the box :) I just have one small nit. Due to the way
> that the virtio stats queue works, the guest emits a stats event with bogus
> values when the balloon driver initializes (which gives the host control of
> the
> channel). Your patches emit this initial event (which contains undefined
> values). In my old code, we kept a boolean flag in the ballon device to
> record
> if stats have been requested and only if that was set would we raise the
> event.
> Without this, the guest can spam the host with an unlimited number of bogus
> events.
Yeah, I've seen this too. I'll fix it. We also need migration and HMP
support. Although the latter seems difficult as we don't have a way for
qemu subsystems to wait for events yet.
> Tested-by: Adam Litke <address@hidden>
Thanks!
>
- [Qemu-devel] [PATCH 3/5] balloon: Drop old stats interface, (continued)
- [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, Eric Blake, 2012/01/19
- Re: [Qemu-devel] [RFC 0/5]: QMP: add balloon-get-memory-stats command, Adam Litke, 2012/01/19
- Re: [Qemu-devel] [RFC 0/5]: QMP: add balloon-get-memory-stats command,
Luiz Capitulino <=