Using the KVM API [LWN.net]

Using the KVM API

Posted Sep 30, 2015 17:49 UTC (Wed) by kvaneesh (subscriber, #45646)
In reply to: Using the KVM API by josh
Parent article: Using the KVM API

With cache=loose, we should used the cached value in the inode in getattr (v9fs_vfs_getattr_dotl). So stat should be fast.

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Using the KVM API

Posted Oct 1, 2015 6:29 UTC (Thu) by kleptog (subscriber, #1183) [Link] (1 responses)

I set up a system locally to run programs under a VM in qemu-kvm with shared folders and it was insanely slow, especially git and find. Stracing on the host showed that for each stat() in the guest, the host was doing a stat() on each directory component. So a stat() of a complete directory tree went O(N^2) on the directory depth.

Now, I get that it's probably a configuration issue since it clearly wasn't caching anything, but I found it really hard to find documentation about qemu that explained this behaviour. On top of that I'm managing them via libvirt, so even if I find a command-line option to deal with something, if libvirt doesn't support it I'm still SOL.

Overall, it hasn't been a great experience, next time I'll probably do what other people do, use VirtualBox or VMWare.

But back to the article, it's a pretty nice interface actually. Hopefully I'll find some reason to use it sometime :)

Using the KVM API

Posted Oct 8, 2015 16:48 UTC (Thu) by LightDot (guest, #73140) [Link]

You can pass raw qemu command line in the libvirt XML. This is an equivalent of '-vnc :30,tls -k fr -no-fd-bootchk':

The VNC option doesn't need to be presented as a command line, I just left it as an example.