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Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to th
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver |
Date: |
Thu, 7 Jan 2010 15:49:18 +0000 |
User-agent: |
Mutt/1.4.1i |
On Thu, Jan 07, 2010 at 09:12:10AM -0600, Anthony Liguori wrote:
> On 01/05/2010 11:08 AM, Adam Litke wrote:
> >This patch has been discussed (and ACKed) in the past, but has not yet
> >been committed due to the congestion surrounding the 0.12 release and
> >other conflicting changes. I would like to rekindle the discussion so
> >that I can make the necessary changes to get this merged.
> >
> >This patch is ported to 0.12.1 and has one issue that I am aware of:
> >
> >It still calls monitor_suspend() and monitor_resume() which I understand
> >is no longer allowed. Does anyone have any ideas on how to enable async
> >monitor commands?
> >
> >+static void request_stats(VirtIOBalloon *vb)
> >+{
> >+ vb->stats_requested = 1;
> >+ reset_stats(vb);
> >+ monitor_suspend(cur_mon);
> >
>
> This bit is not going to work reliably anymore. Really, it never worked
> reliably but this is exacerbated with -qmp since a QMP session will
> never be the cur_mon.
>
> We have a couple of options:
>
> 1) Introduce a query-balloon command that returns immediately, and
> triggers a request for the guest to update the balloon stats. When the
> guest does update the balloon stats, trigger an asynchronous message.
> Asynchronous messages are ignored by the human monitor so they would
> never be displayed there which is unfortunate.
>
> 2) Make info balloon show the last valid stats and have it request new
> stats. Stats will always be delayed but it avoids async messages.
>
> 3) Make qemu request balloon stats regularly (maybe every 10 seconds)
> and display the latest stats with info balloon. This avoids the problem
> in #2 but it means that qemu determines the poll rate instead of a
> management tool.
I don't like the idea of the anything which has hardcoded polling because
it just wastes CPU cycles for the 99% of the time when no one is going to
care about these stats.
> 4) Make info-balloon a proper asynchronous command. We need new
> infrastructure to allow a qmp handler to take a callback that can be
> used to delay the completion of the command. This addresses all of the
> above problems but it introduces a new one. Command completion now
> depends on the guest. This potentially could trip up a naive management
> tool that doesn't realize that the info-balloon command may never complete.
I think 'info-balloon' should be synchronous and without side-effects.
ie return the current stats that QEMU has. We could then add a separate
'refresh-balloon' command + async event notification when that completes.
The tool that is requiring the stats could thus refresh as often as it
likes.
Daniel
--
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- [Qemu-devel] [RFD] virtio: Add memory statistics reporting to the balloon driver, Adam Litke, 2010/01/05
- [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Anthony Liguori, 2010/01/07
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver,
Daniel P. Berrange <=
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Adam Litke, 2010/01/07
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Avi Kivity, 2010/01/07
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Anthony Liguori, 2010/01/07
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Luiz Capitulino, 2010/01/07
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Luiz Capitulino, 2010/01/07
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Anthony Liguori, 2010/01/08
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Luiz Capitulino, 2010/01/08
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Adam Litke, 2010/01/08
- Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver, Luiz Capitulino, 2010/01/08