On 08.06.18, 00:23, "Jim Fehlig" <jfeh...@suse.com> 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).
So far I've seen virtio like any other communication like sockets because on
the host side it is a UDS
and based on that nonblocking I/O would be an efficient way. UDS should also be
reliable like TCP, no data should be dropped
and due to that a writer will block when the data is not cunsumed at the other
end of the socket and the buffer is full.
Another reason from my perspective is that we might get in situations where we
have to send fragments like with any other socket based communication.
But honestly, I don't know what happens inside QEMU, because that's the other
end of the UDS and there might be some special implementation for virtio and
the interconnect between UDS and serial-channel
Maybe a QEMU expert on the virt-tool-list can shed some light on that.
If there is no better/simpler alternative to EPOLL I would prepare the patches
and send them to the virt-tool-list
Regards,
Michael
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