[virt-tools-list] vhostmd - virtio channel support

[Jim Fehlig]

On 06/08/2018 02:30 AM, Daniel P. Berrangé 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 ?

The other transports work that way, but in those cases the guests use the same 
source on the host, e.g. a ramdisk for vbd. For virtio where the source is a 
per-guest channel on the host, I suppose it's best to only send the metrics when 
the guest asks for them.

Regards,
Jim