On Fri 30 Jun 2017 04:22:11 PM CEST, Kevin Wolf wrote: > Am 30.06.2017 um 15:01 hat Alberto Garcia geschrieben: >> On Tue 27 Jun 2017 06:31:45 PM CEST, Kevin Wolf wrote: >> > * Speaking of recursion: ImageInfo recursively includes information >> > about all images in the backing chain. This is what makes the output >> > of query-named-block-nodes so redundant. It is also inconsistent >> > because the runtime information (BlockInfo/BlockDeviceInfo) isn't >> > recursive. >> >> I've also been told of cases where a query-block command on a VM with a >> very large amount of images in all backing chains would slow down the >> guest because of this recursion. >> >> I haven't been able to reproduce this problem myself, but being able to >> see only the devices seen by the guest (as opposed to the complete >> graph) seems like a good idea. > > I think the information only really becomes redundant if you use > query-named-block-nodes because then you list every backing file node > and each of them contains the recursive information. > > With query-block, you start at the top and include the information for > each image in the backing file chain only once. If we did indeed have > a problem there, that might mean that we do in fact need filtering to > reduce the overhead. But I don't think any of the information involves > any I/O to get, so it seems unlikely to me that this would make a big > difference.
Yes, that was also what I thought, but I haven't been able to reproduce the problem so I don't know yet. In my own tests with thousands of backing files I haven't noticed any slowdown caused by query-block. Berto
