Re: [libvirt] [RFC][scale] new API for querying domains stats

On Tue, Jul 01, 2014 at 03:09:13AM -0400, Francesco Romani wrote: > I'd like to discuss possible APIs and plans for new query APIs in libvirt. > > I'm one of the oVirt (http://www.ovirt.org) developers, and I write code for VDSM; > VDSM is the node management daemon, which is in charge, among many other things, to > gather the host and statistics per Domain/VM. > > Right now we aim for a number of VM per node in the (few) hundreds, but we have big plans > to scale much more, and to possibly reach thousands in a not so distant future. > At the moment, we use one thread per VM to gather the VM stats (CPU, network, disk), > and of course this obviously scales poorly. I'll just note here that a bug has been opened for virt-top, which is similar to this. If a domain has a large number of disks (256 virtio-scsi disks in the customer's case), then virt-top spends so long fetching the data for each separate disk, it can take 30-40 seconds between updates. The same thing would happen if you had lots of domains, each with a few disks, but with the total adding up to hundreds of disks. The same thing would happen if you substitute network interfaces for disks. What would help for us: - A way to get information for multiple objects in a single domain - A way to get information for multiple objects across multiple domains