On 08.06.18, 10:31, "Daniel P. Berrangé" <berrange@xxxxxxxxxx> wrote:
On Thu, Jun 07, 2018 at 04:23:32PM -0600, Jim Fehlig wrote:
> On 06/07/2018 09:42 AM, Trapp, Michael wrote:
> > I fully understand the requirements regarding coding style and the way the changes should be split and discussed in detail,
> > but may I ask you to provide some general feedback about the basic concept and if this an option at all before we start discussing the details.
>
> vhostmd already supports 'vbd' and 'xenstore' as transports for the metric
> data. Adding another virtio-channel based transport is a great idea IMO.
>
> WRT writing the data to the various channels, I suppose it is possible to do
> that even if there is no (immediate) recipient for the data? The vbd and
> xenstore transports don't have a protocol so to speak. The data is simply
> written to the disk or xenstore node regardless if there is someone to
> consume it. Can the virtio transport work the same? If so, that would
> alleviate the need for polling all the fds and the static list of
> epoll_event. In virtio_metrics_update() we could simply connect to all the
> channels, write the data, close them, and repeat on the next update period
> (which is every 5sec by default).
Why push it to the guest at a fixed frequency, rather than just letting the
guest query the host at whatever rate it feels it needs ?
content on virtio channel is not discarded. I've setup a simple test and a continuous write on host side blocks when ~123kB are buffered from OS + QEMU.
A delayed read on the VM side contains the whole buffered data.
Looks like the virtio based approach needs a query from the VM to guarantee that the VM get's the current metrics.
Regards,
Michael
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